This is very very easy.
I start with upgrading allied units, then weapons, shields, and repeat. Meanwhile to engine as well a little.
Try to get the tripe shot upgrade before the white orbs, I dealt with them fine.
Awesome game, love it for one that it's a city buildish game, the tower defense addition is great too even tho I'm not all into it. 5/5 tho, keep it up!