How do I do a color filler?

I want to return my blond hair to it's natural dark brown color. I had it dyed back at a salon before but the color wouldn't hold so I went back to blonde. I'm going to dye it back myself using a darker shade than necessary to account for future fading. But first I want to use a filler. I know that a filler is a colorant not mixed with peroxide, but I'm not sure how long to leave it on and whether or not it needs to be washed out before applying the dye. Please don't tell me to go to a salon because they have srewed up my hair so much. I've always had better results doing color myself.Jen