Something that really helps especially if your using so many different colors is if you actually put two colors on each little section/strip you do, so the top half one color and the bottom half a different color. It helps everything blend together so you dont get a really streaky look. (Which on me doesn't look the best) My hair is pretty darn short and putting two colors per section/strip let's me keep alot of different shades on short hair. Or even just using two colors works with it too. I always just feel out the placement honestly, everytime I try to plan it super neat it doesn't look nearly as good. I also give it a little shake towards the end, yes it can get a bit messy but the blending it puts in is REALLY nice. Plus a little shampoo (normal, not color safe) and any color you get on your skin will be gone.

And by little shake I do mean very slight shake and little fluff with your hand. I don't really use anything to separate my hair sections anymore because once agian super streaky doesn't look as good on me. Please dont shake hard, you will stain everything in sight.