Cute game, love the graphics - it gets somewhat trivial, though.
Make sure you have an air missile and artillery ready every time you start a level. Start building 9 apaches, 9 troops and 9 tanks when there's 5-10 seconds to next round. Have an anti-air missile selected to nuke the first few kamikaze planes (a few will probably slip through), shortly hereafter enemy artillery will usually arrive - so you launch your artillery against them. That buys you a lot of breathing room against ground units, so you only have to focus on anti-air missiles against the kamikazes, until you have enough apaches to shoot them down. The reason to produce foot soldiers is that they'll move forward quickly, and attract the kamikazes - cannon fodder
That strategy worked very well for me, but it got trivial so I stopped right after level 25.