Part 2 of 2:
Let’s look at the military tech tree.
Top branch will be your faction, in this case, Vanguard.
The first thing you can research gets you something I don’t remember and the Nanite Injectors mod. Nanite Injectors is a one time per battle heal of 15 plus a short duration defense buff, and a permanent armor buff for the low cost of 5 cosmite (for tier 1 units). It’s a “leave one point” action which means you can use it and still do a “single action” or a single attack. This doesn’t look like much at first glance but its cheap and early and will increase the survivability of any Vanguard unit that you want to take a hit. So don’t use it on your cheap troopers, but it’s great on your PUGs/Engis and Laser Tanks.
Second thing on this tree gets you the Engi, which you do want.
Third thing on this tree is the Gunship, on which I will do another post later (properly modded Gunships rock forth, but they are tricky to get right).
Fourth thing is Laser Tank. That will be enough for most games.
The vanguard branch has some sub-branches. Of note, see the one that gives your Engineers a Missile Turret instead of a Gun Turret. This may not seem like a big deal but the Missile Turrets are AOE and they demolish cover. Engis with missiles rule.
The two branches below Vanguard are your weapon types, Laser and then Firearms.
In Laser, you will see the tier 1 adds a Burning debuff to your laser attacks, which stacks nicely with the Promethean special tech. Laser techs are mostly generic IMO except for the Precision Lasers (which adds damage, to hit, and range) and the Disintegrator one (very late but very mean).
In Firearms, on the second step you will see Rail Accelerators which costs the low low price of 5 cosmite for a tier 1 unit and adds damage, to hit and range to your attacks. This is your friend, for Troopers and Gunships especially, as well as firearms hero. Range is good. It’s “one longer”. There is another Firearm mod later on that reduces the penalty to hit from cover and units in the way which is also very nice. I think there’s a Stagger one as well and Stagger is good.
The bottom branch on the tech tree will be your special tech. It’s a good idea early to look at the early special techs and try to see the synergies with the other stuff you have going on. For example, Synthesis has a tier 1 tech that makes all your mechanical units (like Engis, PUGs, Tanks and Gunships) get the Synthesis Integrated bonus. Or, Promethean has a mod that does extra damage to stuff that’s on fire, which works with laser mods, etc.
These are just some examples of how to look through the tech tree and try to see what works, what goes with what, etc.
I cheated b/c I picked the Vanguard which is easiest to grok. I still have no clue on several of the other factions.