Just take your time aiming. There doesn't seem to be any major penalties for losing friendly units. I like to rotate 90 degrees and hold down until I come to an enemy, then I take my time and line up the shots. If they are coming towards you just fire continuously and hope some of them hit the guy because you won't have time to aim.
The bombing missions are pretty easy like the train one. If you just destroy the first carriage the train will stop, leaving the rest of them for your picking.
-squiffyboy