The first thing you can build is a reactor. build it, maybe put it off a corridor. Note that if an enemy hacker bot gets into your reactor, they can shut off the cooling and devastate your base, ending the game if you're not careful.
Immideatly after beginning construction of the power plant, you gain the ability to construct the rest of your primary buildings- Drone Fabricators, Bot Factories, Power Pylons and Iron Extractors. From this point on, it is a race to the Thorium on the field. Without Thorium, you are at a severe disadvantage, as your power is more limited and thus research and mining goes slower. Your enemy can gain a real edge on you if you don't get enough Thorium. In a game starting with 7, you need at least 3, and you'll tend to get this much. Getting the 4th is icing on the cake, but you don't really need it. However, it can put your opponent in a bad mood, giving them the idea that they're going to lose, so you will have psychological edge.
Because of this, you're going to want a drone fabricator, and at that, maybe two. They only cost 100 Metal and each drone is actually free... so pumping out several drones quickly could be a very good idea. It is also good to keep a stack of drones on hand in your base, as they are free and are used to expand your resources.
It is also a good idea to begin research right away. Don't build iron extractors yet- you start with plenty of iron and you might not even need a starting army. Research whatever you want, as better weapons or different unit types might be the edge you're looking for.
Wait until you have some thorium before building Iron Extractors.

This game offers something that most other RTS games don't, and I'm sure that's why you're here. When I first started playing this game, I saw it as more of a novelty than a necessity, but if you want to win, microing your units with FPS mode can really give you a big advantage in a battle. If you can help it, never let your units battle alone.
First of all, you are better than the AI. You can still give your units basic commands while in FPS mode (F for follow, G for Guard).
Second of all, you have great range. You can finish a battle before it starts by sniping enemies, even with a weapon intended for normal battle. When my friend started consistanty beating me, I really didn't understand why, and neither did he. I had great research, map control, and power diversion, but it turned out he was first personing every battle and thus giving his troops a large advantage.

This is entirely up to you. Practically every technology will give you some sort of edge. Other guides seem to give you a tree that you should follow, but the only way to devlop what is best for you is to experiment. There are only a couple points of advice I can give:

1) Research better weapons to give yourself an edge over the opponent.
There is a very large variety of weapons in this game, each with their own pros and cons. I will talk about weapons specifcically in the weapons section, but know that better weapons=more kills. Try to stay away from the machine gun weapons, as they don't appear to be very useful.

2) Don't research better bots. This is not a permanent rule. If you read the information about robot armor, you will see that it only protects against physical weapons... meaning bullets and missles. This is useful once you have finally beaten back your enemy and are ready to infiltrate his/her base, but on the battlefield it is vastly unecessary. The research time coupled with the slight expense makes them a bit incapable compared to smaller bots. However, hitpoints are increased in the third teir. Consider them for normal battlefield play if you have enough iron.

3) Should you find yourself in a position where you don't have much Thorium in your reactor, research the mining upgrade in the structures tree to improve your iron income wihtout having to expand.

Bots
Pros
-Can actually win you the game.
-Are cheap.
-Are quick to produce. (4 at a time if you have the resources)
-Can be carried in transports.
Cons
-Are Slow
-Are easy to destroy, and tend to clump up.

Tanks/Walkers
-Faster than bots
-Have greater range (though in FPS mode, have same range)
-Much harder to destroy
-Can be mounted with cannons
Cons
-Sometimes cannot shoot downward. On top of a hill, they cannot defeat bots.
-Can only assist in the inside of an enemy base if your opponent has not added corridors to their main entrance. Thus alone they cannot win you the game.

Planes
-Very fast, can assault a position quickly or provide quick reinforcements
-Can swiftly attack enemy artillary
Cons
-Hard to control in FPS mode
-Cannot alone win you the game
-Are easily destroyed

Energy weapons are a good choice because they arent affected by armor. In this category are Pulse weapons, Beams, and Focused Electron Beams.

Pulse are your basic energy rifles, and they are my weapon of choice. They have decent fire rate and high firepower, and are great for first person sniping. Consider Researching pulse as your early troops' primary weapon.

Beams are useful for lots of bots, and in first person mode, can work wonders. You can simply spray a group of bots with a beam weapon a few times and watch them explode. The AI tends to do this sometimes. Consider Researching beams as your early troops' primary weapon.

These are in no way your primary weapon. Just want to make that clear. However, if you're looking for snipers, snipers that you don't even have to micro, look no further. They take a long time to reload, but can one shot planes and infantry, and deal heavy damage to tanks. Consider Researching Focused Electron pulse as your troops' primary support.

Ballistic weapons are pretty useful. They can be canceled out with armor, however. Should you see your enemy using a lot of ballistic weapons, that is the time to begin armoring your troops.

Missles are availabe to help annihilate tanks and do good damage on doors. They have very decent splash damage, and can be carried by aircraft as well. Consider researching missles as a good support weapon.

Phased Mass works well as antiair for those quick fighters, and is also strong against bots without armor. Personally, however, I have never had a case where phased mass or heavy phased mass benefit me, so I'm going to have to reccomend against it. However, it can do well against aircraft.

Timed explosives are useful as grenades. Often times an enemy strategy is to hide behind the first door of their base. After equipping it as a bot's special ability, enter first person and use 'Q' to throw it.

Only equipable to tanks, they have very decent strength, range, and accuracy. However, their reload time can be a bit high. But, good news! You can research technologies that cut down this reload time.

Trion weapons are game ending weapons that give you a distinctive edge over your opponent on the battlefield. They have the highest damage in the game, but have a slow reload time. You can research technology to make this time a bit quicker.
It is also important to remember that one cannot simply bestow Trion weapons to all of his/her troops. You must generate trion by dedicating power to it, and this makes it a limited resource. Thus, although they make a good primary, cannot really be used as your only weapon. Keep in mind, also, that should one not have a lot of Thorium, this is a poor choice of weapon, seeing as how a player must dedicate a fraction of their power to create it.

Using up all of your power is very easy as a beginner, but as you gain experience, you tend to want to keep it all in check. However, you will soon realize that to become entirely effecient, using all of your power but not a bit too much is your best bet. For this purpose, you are given a reserve power area. With this, you can live beyond your means for a little while.

You can add power to Defences, Forefields, Trion Extraction, Iron Extraction, and Research.

It is a good idea to keep using all of your power at all times. If you are producing 70 power try to always be using 70 power. If you find yourself with a surplus of power, be sure to keep researching and turn up your iron or trion extraction. If you are under siege, turn up power to defences. Note: turning up power to defences also affects your base's buildings. It makes the clocks on your buildings tick a bit faster, so if you're trying to summon another meteor out of the sky quicker, that would be way to do it.

I've said earlier in the guide, try to get an edge on Thorium. Meteors will crash (or you can summon them with the radar building) that contain more Thorium, so its a good idea to put more of them in your reactor. Keep in mind that Thorium is your primary bottle neck in this game.

Do not over expand! I know a lot of you crazy RTS people will be quick to use your free expansion, but keep in mind that for every Iron Extractor you have, this affects your power. If you get too many, you have to turn down your iron extraction far below effeciency, which makes it questionable if it was even worth building them in the first place. Save it until you have the trion.

By the way, as for my thoughts on starting with less than 7 trion: It doesn't seem to add any strategic prowess to the game, just makes the game longer. I play with all 7 trion starting on the map.