Tactics boil down to risk mangement, as any rng games does, but imo this game gives you enough options to consider using.
The thing is, you have to stack the odds in your favour incredibly. Consider anything under 70% to hit as a pot shot to be used if you have no better options. And if you miss, is there a contingency (a rocket launcher in range/a support with smoke/other friendlies can move out of harms way etc)
Personally I found normal difficulty perfect for a first playthrough to "get" the game, and classic ironman as a "real" playthrough (i did try classic first but had to quit). Tried impossible ironman.....surviving a mission is a grinding drudge of risk management extraordinaire. made one mistake (moved one squad memeber one square too far...alerted two seperate groups of skinnymen (groups are larger in impossible as well)... and lost my entire squad without firing a shot. Any shot in the open or even half cover is basically an insta-kill, and you do less damage. Needless to say I didnt try that again.
The main issue is the first half of the game is far more challenging and exciting than the first, then it becomes a bit of a turkey shoot as long as you don't take adverse risks, even on classic. It would be perfect if they maintained the difficulty throughout for each respective difficulty somehow.
As for your squad...
- The most important stat it the aim one. Pick and choose members with higher aim stats wherever possible.Get scopes for all your members. And *always* go for the shot with the higher chance to hit.
- Consider heavies purely as rocket launchers/grenade carriers and level up in that regard.
- know who you would sacrifice if you had to, I would have one or two in every mission with specifically selected red armour, usually assault rookies with grenades.
- start leveling a sniper as soon as possible
Personally, my favourite squad ends up being (IIRC)
1 sniper - doubletap squadsight pistol
1 heavy - 2 grenades (or shoot twice), shredder, rocketeer
2 or 3 assault - lightning reflexes, 2 shots, within 4 reaction.
1 or 2 support - move faster, deep pockets, medic
I do find assaults with rifles the most useful, but the one sniper absolutely critical. In fact, the game would be near impossible without one.