I always buy a few shades darker than what I actually want.. in a few washes it'll fade close to the color I wanted. This is especially true for auburn colors. I always dye my hair auburn.. trust me, just let it fade. Otherwise you risk just having oddly color orange-red hair.
dont leave it on as long?...it's the length of time you leave it on that makes it darker if you rinse it out sooner it won't soak up so much color but don't shorten it too much or you won't keep the color for as long either...fine line here