These are the five topic of this guide:
1. Game Settings
2. General Things
3. Air Micro
4. Land Micro
5. Build Orders
6. Maps

About me:
My name is Nausicaä (often エリン) it is from an anime. I'm about 20 years old and from Germany, that's why my English isn't really good (I make often small mistakes...)

Sadly you can't change the short cuts in Supreme Commander 2, but normally you don't need them anyway (short cuts[supcom2.wikia.com]).

Some common problems:

• If you can't move in a game lobby the host is normally alt + tabbed.
  
• If you have a 0 ping to another player than you, the game won't launch (press alt+f4 and then no, if the game is stucked in the lauching process) rejoin the lobby a few times and the prob is fixed.
  
• Another reason for not launching is when one player is alt and tabbed in the moment the game is launching (in this case you have to wait).
  
• If you want to write to other players before all players have loaded, you can press enter to open the chat. However, don't give build orders already because the replay will be destroyed.

Basic game settings:

• No exclusions (because the game gets unbalanced)
  
• Victory Condition: Assassination
  
• Spawn Position: Fixed or Random
  
• Rush Timer: Off
  
• Fog of War: Explored Terrain/ No Units
  
• Game Speed: Normal
  
• Observers: None or Allowed

In some maps it is clear what you should do. The back player is normally doing air, and the front player normally does land. If you're not sure or if the map doesn't show it clearly ask your team or just make what you can do best and tell your team early what you're doing.
In 2v2s there is normally one air and one land player.
If there is water it is somewhat more difficult and I'm going to explain this in my advanced guides.

Some useful tips:

• Do not build walls of PD even though it works against the AI, a player will just go around it or outrange it.
  
• Only training has an effect on experimental units (expect buildings).
  
• Always have a scout (every 1-4mins) or a radar for vision.
  
• Adapters or P- Shields in a big buch can stop a lot of bombs and air.
  
• Destroying units does not only give veterancy for your units, you also earn Research Points!
  
• Always save a few Research Points in case you need to research something unexpected (for example, you might research hunker to avoid losing your ACU).
  
• Remember that in Assassination mode the goal is to destroy the enemy ACU. Even if you have almost lost you can still win if you can snipe the ACU before your ACU gets destroyed. Don't give up too fast.

Some details about the different units[supcom2.wikia.com] and the research system[supcom2.wikia.com].

Basic air micro:

• In air fights: Select all of your fighters and press "a" to issiue an attack order, then click the ground beneath the air fight, repeat this so your fighters shoot the best target.
  
• If you bomb press "s" and give a new move order, so the bomber doesn't fly stupidly around over anti air towers or units (aa's).
  
• Have a good map awareness (and a radar).
  
• Try to attack enemies fighters while they bomb (then your fighters get behind the enemies air, so they can't shoot back).

Some more infromation:
Nephylim's Micro Guide

Land micro:

• With control and right mouse button your tanks will try to bunch up.
  
• Use your ACU in the early game as a shield for your tanks (repairing costs nothing) but make sure that your ACU doesn't die.
  
• Don't get hit by mobile arty! (when you see them shoot, change direction)
  
• Move your bots fast in different directions because they can dodge attacks and use them to flank your enemy because they're faster than tanks.

Some more infromation:
Nephylim's Micro Guide

General:

• UEF: Always research built costs for structures.
  
• Cybran: Build time and costs needs many research points in the early game, but it is really effective.

Build oder:

• Build the four starting mass points (2 ACU and 1 each engineer); expand your mass with the engineers and built with the ACU first your factories and research and then 2-3 energy.
  
• Don't forget to built many energy in the mid and late game when the mass points get more effective.
  
• As Land you can start with three land factories or 2 land factories and one research station or with one land factory and two research stations or just three research stations.
  
• As Air you can start with two air factories (and one research) or with two research stations and one air factory (big maps).

This guide isn't complete, but these are some basic built orders and following those should improve your playing a lot.
Edit: You can start right away with a factory because you have a huge starting mass (on small maps like most 1v1 and 2v2 maps).

Some more information (especially for playing without dlc): Redarrow's Guide to Standard Build Orders.

Some general stragies for some often used maps.

I know that I didn't talk about many important things like ACU rushing and how to defend against it or TML (aoen) or many other things, but that would be too much at once I think. I'll make another guide series (advanced guides) as soon as I have some time. If you would like me to talk about any topic leave a comment.
All in all I hope you enjoyed the guides and more importantly that they help you in the game.
Special Thanks to:
Shade for all the help and support!
Complex for checking the written content!
Aussie for proofing!
As well thanks to all who played with me in the games I used in the guide :)
And thank you for reading!

Edit: Infromation will be added and the guide will improve.