Get High Amount of Plasma
The best way to get alot of plasma is to get combos right? well your best form to do that in is the lizard thing form and jus keep jumping on the enemies and get those lvls up the best level to do
this in is when you first find some.

Get More Plasm
To get more "Plasm" points from each kill, get in as many consecutive hits as possible. The more consecutive hits you get, the more damage you do and the more plasm you get from each kill... which essentially means more powerups faster!

Highest hit chains
During the first few levels after your forms are taken there are a number of spawn nodes that resease basic drone and gunners. these pose very little threat. when you find these you shouldn't destroy the node. you can continue to kill the drones with out being damaged. if you only use X you can get more than 150 hits in a chain before the node runs out of people and destrys itself. in the beginning of the game this is the best way to get alot of plasm early on.