From: Berlin, Germany
1. Look at the AARs from Telemecus/HLYA, they have good descriptions. Also, the user beender has gotten top notch results on T1 bombing, maybe you can ask him
2. Basically, fly ground support only for important battles to keep your air force fresh and rested. Pretty much what you would do IRL.
3. Rail lines, hex ownership nearby, enemy units nearby, length of retreat path in hexagons, cost of retreat path in MP, general direction (east for USSR, west for Axis) and some more.
On a German wargaming forum I once made an attempt to lay out what I think the priority list is but there were always exceptions (5-10%) I cannot explain so I am careful creating such a list. Fearful of the actions for damage when a little anomaly spoiled your game winning mega pocket. The best advice I can give is to get an idea for yourself by playing/by dedicated tests. Without guarantee on that, you can start your tests with the assumption ZOC>Hex ownership>rails>general direction
Maybe other players have figured out the algorithm in its entirety.