When I dye, the only thing I like to do is clean the surface with rubbing alcohol or deglazer.
When you apply the dye, start in a horizontal direction, second coat go in a vertical direction, then on a third go diagonally. This should eliminate the streaking. The stolman book on coloring leather explains it better.
Just start out with lighter colors. Thin your colors out so the color does not get too dark. For oil dyes, I usually use a 3-1 mix of 1part dye to 3 parts NF oil.