I think your cases are too general and dividing them will help you to deal with them easily .
I will assume you have different soldier classes , just for clarification .
That depends on many things :
1. Positioning, use cover/walls depending on known position of hostiles (probably hardest to implement)
Is the teammate taking/not taking fire ?
Heavy soldiers prefer close cover , Snipers prefer far ones .
Is the teammate injured ? if so he will need to take the closest cover to the medic .
Choosing High areas to expose as many enemies as possible .
Choosing Hidden areas to make surprising attacks .
You must prioritize your conditions (time , safety , superiority , close / far ... etc) , that will help you determine which position to choose for every situation .
2. "Plan" usage of timeunits so doesnt end turn in exposed location
That will depend on how far is the your soldier , armored/weak enemies , covered / exposed ...
3. Pick suitable firemodes (snap shot, aim fire, full auto) depending on "situation"
I think of something like :
4. Choose when/if to use special actions like throw grenade, crouch, heal teammates
Fighting group of enemies ? -> They are far ? -> Throw grenade , They are close ? -> open heavy fire .
Going to positions A ? -> Crouch if that will help you hide from enemy's sight , getting to narrow areas or when getting behind cover ...
Check for close teammates ? -> if no one injured -> check for far ones , if a close teammate is injured go help him . Here you will have to make the other teammate come closer to the healer as well as the healer will go closer to him (if possible) . Also you must make conditions about who will get treated first (closer first or critically injured first ...)
mmm , I suppose chasing enemies will be better if the team is in superior condition , if not then they will have to retreat instead .
5. Choose weather to run after enemies, stay put, scout for additional enemies when noone is visible etc.
Staying will be preferred if you want to ambush the enemy when he comes to your area , or to hide from scouts .
Scout for enemies while your team is recovering from a fight for example , so you can get ready as early as possible .
There are so many conditions and variables here , I think you'd better play XCOM for some more time and try to draw a tree or something to define the situations and actions .