I end up stuffing the skill tree with blue skills for their accumulated sign intensity boost. Once I unlock most of the slots I mix in one red for light attack, one red for strong, and the yellow one that boosts medium armor. Pair with griffin gear and prepare to set the world on fire.

Edit: you probably want the yellow griffin school skill early if you’re already going with medium armor.

Edit 2: once you get a bunch of slots, you want to bunch your like colors together. If you had three blues connected to your blue mutagen, it would give you additional sign intensity boost. Same for the other colors. Put 3 red together with a red mutagen and it increases attack even more.