- You don't need to worry about the Avatar counter until it's pretty full. Just make sure you have a story mission or facility available you can run before it gets to the max. If it does max out, you still have 28? days to do something about it before game over.
- Skull jacking an officer unlocks the cortex, which will not show up until then, and is a bit of a pain in the ass. It's okay to put off doing this for a while. They become easier to deal with once you have better weapons and/or psi troopers
- The next mission in that line also unlocks a new enemy type, that's also kinda scary.
- Evac when needed. If you have someone bleeding out and no med kits available, you can have someone pick them up and evac them before the timer runs out to keep them alive. You can still try to complete the mission with the remaining troops. Or if it's gone sideways, or you spotted a particularly scary group of enemies, you can scrub the whole mission. I haven't seen any failure penalties that are really that bad yet. It's usually just a lack of reward. Getting some XP and keeping your soldiers alive is so far always better than getting the reward and losing experienced soldiers.
- Prioritize the guerilla warfare center, or whatever, for the squad size upgrades.
- Grenades are awesome. Until mid-game in my current game, it was pretty rare for me to finish a mission with any remaining. Sometimes I'd pack double grenadiers for the extra explosive punch. They're guaranteed damage against an enemy, and they destroy cover to line up later shots from your squad.
- Psi-troopers are OP