I have a strategy that mostly leads to victory: do not buy upgrades, that are useless when you try archieve briliant rating, like +1 gem or scorching treasure or return portal. Have a constant money supply by maxing mp recovery and make your tree cutting skill cost 50mp and give you 100 gold. Also, start game by firstly putting towers on mana springs. Max out meteor cost and frenzy master. I prefer using undead chilling crypt, so maximize every skill involving it. If you see strong enemies coming - prepare to use frenzy, if any of ninja gets past tower blockade( they can stop ninjas by using fear or freeze) - use meteor skill. In this way, you can have briliant ratings early in the game without any bigger effort. Cheers!
Moving a little as possible? i think it would be pretty hard to do all the time. It's better to max out your firepower by upgrading spread and then anything else, but i prefer critical. In this way they couldn't reach you even in higher level, also remember to always have blue "bubble" upgrade - it is one timer that shields you for damage. Watch out and do not upgrade any of pixels and points upgrades.
Shock tower for the win! Guard tower is some kind of lazy and weakass tower, but once you level it up to 4th level with help of 'battle standart' subclass - additional experience, you can level it up up to level 10! try it out!