It is crucial that you have dead-eye accuracy in the harder difficulties as you only have a handful of explosive weapons available. Use the Easy difficulty to hone your skills.
Help
Although there is no playable tutorial for the game there is a 'Help' option at the 'Main' menu which will bring up a text and diagram guide which you will find useful.
Improve Aim
Flying slower will improve your aim significantly, the only problem with ths though is there's more of a chance that anti-aircraft guns will turn your plane into a flying sieve.
Soldiers
Try to pick off enemy soldiers whenever you can with a bombing raid or machine gun fire as they can rebuild enemy defences.
