So I created a compilation thread over on the Paradox Forums and to ensure it helps the masses I thought I copy it here to in an organised fashion.

BattleTech is a strategic turn-based game with mechs and most of the BattleTech Universe in the game's settings is controlled by 5 power house.

Background
Humanity was united by a single interstellar government called the Star League. This was ruled by House Cameron, until they were destroyed. In the aftermath, the five great houses - Davion, Steiner, Kurita, Liao and Marik - all claimed the right to rule the Star League and started a series of conflicts called the Succession Wars over it. This game is set in 3025, just after the Third Succession War.

Each of the Great Houses has carved out their own realm. Collectively these realms are known as the Inner Sphere.

House Davion rules the Federated Suns
Probably the easiest faction for a typical American influenced Western audience to see as The Good Guys. House Davion values democracy and liberty, and kind of loosely resembles the United Kingdom with its constitutional monarchy. They can still be jerks like everyone else is though.

House Kurita rules the Draconis Combine
Fedual Japan in space. No, really. Like with samurai and everything.

House Liao rules the Capellan Confederation
China and Russia together, in space. Remember how BT came from the Cold War? Yeah, these guys are the autocratic, secret police who vanishes people faction. It doesn't mean they're all bad though.

House Steiner rules the Lyran Commonwealth
The Lyrans are known for their commerce and industry. Though, their military is often held back by commanders being chosen for political reasons rather than strategic competence. Their culture is predominately German influenced.

House Marik rules the Free Worlds League
Marik never appears in the games, so I hardly know about them. Sarna says they're fond of democracy. Images suggest they're overly fond of purple.

Comstar
A secretive organization that controls interstellar communication, and guards knowledge by building a religion around it. Claims to be neutral but has been doing all kinds of clandestine stuff.

The Periphery
The area of space beyond the Inner Sphere. The Great Houses still have an influence here, but there's a lot of minor players as well, and pirates. Obviously.

The Clans
Soon.

1. Figure out your loadouts and skills so that mechs complement each other and can work together. For example, have two close range mechs, one longer range support mech, and one faster flanking mech.
   
2. When outfitting your mechs, use the parts from the dismount window first as this will reduce the time for your mech in the bay.
   
3. Know your weapons, their effective ranges, what skills complement them. Know which weapons have minimum ranges, and what they are.
   
4. Have a plan on how you want to position your mechs so that all of them attack at their most effective ranges. Front line fighters need more armour, while ranged fighters can survive with less.
   
5. Don't over cool your mechs, having a heat neutral mech (like the default Shadowhawk) is an under gunned (or under armoured) mech.

1. When you drop, study the terrain, figure out the optimum location to position your mechs for maximum effect. Think of where you want to fight the enemy. (Can you get there? Can you force the enemy to go there? What direction do you want to approach from, what cover is available to you, what cover is available to the enemy?)
   
2. Use every positional advantage to force the enemy into bad positions and/or bad trades.
   
3. That if you plan to shoot at a bulwark-ed enemy, and you also plan to melee them, use the melee attack first.
   
4. If your mech is already bulwark-ed and has evasion pips, maybe you should reserve down and make them move first. Potentially firing on your mech which is already in a tactically optimum spot to be shot at (unless he’s going to melee you).
   
5. In other words, think through these factors - don’t just move your mech when it’s your turn in some random order.

1. Particularly its ability to negate bulwark and ignore evasion.
   
2. Thus, you shouldn't be pro- or anti- melee (I’m looking at you, streamers) you should use it as appropriate.
   
3. DFA is extremely powerful - you will take leg or armour damage (not maybe take, you will take <- streamers are confused on this). Every mech with jumpjets could potentially DFA at least once safely if you keep your legs in good condition. This is an extremely powerful attack and shouldn't be neglected.
   
4. If you are in close range with the enemy and are in a mech that has been building up heat, consider spending a turn doing melee, punching the enemy instead of firing weapons. This can be an effective attack, not incidentally removing any evasion from that enemy, and will give your mech time to cool down.
   
5. If you do decide to melee/punch an enemy mech, do it before you fire on the mech with your LRM and SRM mechs, again so you can hit the hole your melee attack will make with those missiles.
   
6. Watch out for them doing it to you. Any jumping mech in melee range is very dangerous. Don’t forget that.

1. Multi-target is really good when used to remove evasion pips.
   
2. Multi-target is really good when paired with breaching shot (ignores braced for a single weapon) - if a mech is carrying 2 or 3 high damage weapons against an enemy force that happens to be braced, he can multi-target each one of them for max damage.
   
3. Most streamers aren't using sensor lock at all, or if they are, not very well. Sensor lock lets you remove two evasion stacks. Isn't this a better use of your Spider mech in some situations than shooting a target with 5 evasion stacks? Again, think about move order. It’s also really good for shooting beyond visual range.​

1. Most people use Precision Strike a lot. This increases your to-hit percentage by some, along with calling a shot but don't overuse it.
   
2. Vigilance is your friend and a lot more powerful in many circumstances. You can move to get evasion, brace to get guarded, and shoot.
   
3. 50 Morale gives a +1 hit for all your pilots, so don't waste morale needlessly.

1. Generally, you should manage your heat. However, deliberately overheating and taking structural damage is NOT BAD in situations in which the alternative is likely taking more catastrophic damage from an opponent you do not bring down. Being heat neutral may make your inner OCD spectrum happy, but if it means you lose more arms, torsos, legs and mechs because you don’t down the opponent fast enough, then you are playing poorly. the little bit of internal damage you take from deliberately overheating is ~40k of repair costs and 5 days in the shop. Totally worth it in the right situation.
   
2. Similarly, there is a right time and wrong time to DFA. The excessive concern about damage to the legs is not worth it when the DFA will clear an otherwise really dangerous mech from the field.
   
3. Similarly, there is a right time and wrong time to worry about getting shot. You WANT the enemy to shoot at you when you have lots of evasion and are braced. So, for god’s sake, don’t freaking move (reserve your turn!) when you are in that state until the last opportunity you have to make that move.

1. One example is constantly overused - I reserve down my light, then I move in, shoot, and move out. It’s not really that powerful, and its rare where a situation really benefits from that. Not saying to ignore that tactic, but that’s really not the point. This also works out better if your pilot has the Ace Pilot skill.
   
2. The real benefits of reserve are to try to make the opponent react to you, rather than you react to the opponent. A good example was the one I gave above, where you have a mech in a really good defensive position. Don’t move that mech until you MUST, because it gives you the most tactical flexibility.
   
3. Learn to use the reserve button. It is usually better to let the enemy move before you do, so you can respond to their movement, instead of them responding to yours. This lets you get more advantageous positioning. It is ESPECIALLY useful to reserve the actions of your light mechs and scouts.

1. Moving your mech to get no pips of evasion is a waste of a move.
   
2. You should always move before firing whenever tactically possible to get maximum pips of evasion. If you have the bulwark skill, the other option is to not move at all. Moving minimally is useless.
   
3. Movement distance depends on the engine of the mech. A Centurion has a relatively light and thus slow engine but lots of room for weapons. A Shadowhawk has a much heavier engine which makes him faster but leaves less room for weapons. The actual movement distance can also be reduced by the terrain you are on. Woods, Water, Rough, and Forest for example impede your movement. The most important factor is still engine rating.
   
4. If you have good long ranged weaponry and the enemy does not, let the enemy come to you. By the same token, if your mechs are loaded to the brim with short range weapons, you probably do not want to loiter at long range with an enemy that has good long range firepower.
   
5. When should you move, and how?

• If you don’t want to bulwark.
  
• To maximize pips of evasion via maximum movement before firing.
  
• Jump if you can afford the heat, you get even more evasion that way.
  
• To rotate your chassis to spread damage. If your left side is hurting, rotate so their next shots are likely to hit the right side.
• In order to change the focus of the enemy’s fire. Putting a stronger mech into a more vulnerable position to take the heat off a weaker mech can work, if the opponent isn't paying attention - or if you are skilled - by making the weaker mech only target-able by making the opponent vulnerable themselves to get at it.
  
• To flank an enemy in cover/bracing or to focus on a particular weakened side.
  
• Move under cover (or concealment) advancing over open ground is normally not a good plan.​

1. Critical hits are two-stage - the first crit damages the weapon and makes it less accurate, the second destroys it. Orange for damaged, red for destroyed.
   
2. You never, never, EVER put ammo in the CT (Center Torso). A crit blowing up your ammo will destroy the location the ammo is stored in. If this is an arm, a leg or a side torso, your mech lives on. If the ammo blows in your CT, your mech is dead.
   
3. Lighter mechs get to move first so use Initiative to your advantage. Reserve while safe then shoot when he gets to move last. You can then move back into a safe spot.
   
4. Multi-target and Breaching Shot - if you attack three targets with only one weapon each, Breaching Shot will trigger for each attack.
   
5. Use Missiles first to remove Evasion as they're more likely to do actual damage thanks to each Missile having an individual roll.
   
6. Vehicles will die if any one section loses its structure.
   
7. Mechs will die if: both legs are taken out, head, or the CT.
   
8. The main character can't die.
   
9. If a friendly pilot is incapacitated the chances of death are as follows: 90% - (Guts * 5%) or if the cockpit is destroyed 140% - (Guts * 5%).
   
10. Focus fire. As the enemy mechs are identified, look at their loadouts, their armour placement, their ammo placement. What is their optimal range, can you exploit that somehow? Identify the greatest threat and eliminate it. Also worth shooting at the ammo locations as you get more BANG for your buck. Once incapacitated, move onto the next biggest threat.
    
11. Knocking mechs down gives you automatic called shots (unless you multi-target) which provides same a similar effect as Precise Shot without using morale/knocking the enemy down an initiative phase. Knock-downed mechs always land on their backs. Combine this with a manoeuvre to get a side shot to focus fire into the section you desire to be, no more.
    
12. Remember this isn't X-Com! The game play is a lot different and you will need to use many different tactics for the situation.

1. Energy - Generates as much heat as they do damage but no ammo issues.
   
2. Ballistic - Are great at knocking mechs over and generate little heat. The bigger the number the shorter the range.
   
3. Missiles - Are great at the range they are made for but rubbish outside of it. The bigger the number, the more missiles are fired.
   
4. Support - Flamers, shared with small lasers, and machine guns. Support weapons fire when engaging in melee and always ignore evasion pips. Flamers in particular can shutdown opposing Heavy/Assault mech's through overheating them.
   
5. Weapons that have long range like PPC, Large Laser, AC10, AC5 can shoot people out of your vision range, you can check their in-game range, and LRMs and AC2 have extreme range. You can manipulate the spotter initiative with reserve option to get the most out of your snipers.

• Recruit - none
  
• Gunner - Multi-Target (Gunnery Lvl 5)
  
• Pilot - Evasive Movement (Piloting Lvl 5)
  
• Defender - Bulwark (Guts Lvl 5)
  
• Tactician - Sensor Lock (Tactics Lvl 5)
  
• Lancer - Bulwark, Multi-Target and Breaching Shot (Guts Lvl 5 / Gunnery Lvl 8)
  
• Scout - Evasive Movement, Sensor Lock and Master Tactician (Piloting Lvl 5 / Tactics Lvl 8)
  
• Skirmisher - Multi-Target, Breaching Shot and Evasive Movement (Gunnery Lvl 8 / Piloting Lvl 5)
  
• Recon - Evasive Movement, Ace Pilot, and Sensor Lock (Piloting Lvl 8 / Tactics Lvl 5)
  
• Vanguard - Bulwark, Sensor Lock and Master Tactician (Guts Lvl 5 / Tactics Lvl 8)
  
• Brawler - Evasive Movement, Bulwark and Juggernaut (Piloting Lvl 5 / Guts Lvl 8)​
  
• Gladiator - Multi-Target, Bulwark, and Juggernaut (Gunnery Lvl 5 / Guts (Lvl 8)
  
• Outrider - Bulwark, Evasive Movement and Ace Pilot (Guts Lvl 5 / Piloting Lvl 8)
  
• Sharpshooter - Sensor Lock, Multi-Target, and Breaching Shot (Tactics Lvl 5 / Gunnery Lvl 8)​
  
• Sentinel - Sensor Lock, Bulwark and Juggernaut (Tactics Lvl 5 / Guts Lvl 8)
  
• Flanker - Multi-Target, Evasive Movement, and Ace Pilot (Gunnery Lvl 5 / Piloting Lvl 8)
  
• Striker - Multi-Target, Sensor Lock, and Master Tactician (Gunnery Lvl 5 / Tactics Lvl 8)

There is also Driver, but that is just for the AI.

BattleTech Community Made Game Guides[forum.paradoxplaza.com]
Spreadsheet of BattleTech Knowledge[docs.google.com] by DrDodger/Voranth
10 Essential Top Tips for Beginners by PartyElite
Early Pre-Campaign Strategy[forum.paradoxplaza.com] by Panpiper
Cyttorak's Illustrated Tutorial[forum.paradoxplaza.com]
Eck's Tactical Combat Guide
Discord[discordapp.com]
Twitch[www.twitch.tv]
Sarna[www.sarna.net]

To all those that commented on the many BattleTech youtube videos, Joanna/G from the Paradox Forums and the many other contributors there. Ortinoth from Twitch for providing data for the spreadsheet.

To gain more contributors for this guide, along with adding pictures and more tips for PvP.