Quick question (On prismacolor markers)

Hey, I draw a lot of anime. and I just got a set of prismacolor markers, and i'm having problems with value. I've tried using different shades of grey over and under colors, and tried using a darker shade of the same color. If anyone has any suggestions they'd be greatly appreciated.

post a picture and we'll start from there. you can go over the same colour twice to darken it. you can use complimentary colors to darken it, gray over a color will cause mush and could flatten an image.

Complimentary colors!!! Why the fuck didn't I think of that