A common mistake it over lightening. You will most definately run into problems if you are trying to get too many levels of lift, and hitting your target right off the hop. You must go back to the basics, find the underlying pigment of your target shade, and aim for that when removing build up. I watch stylists over-lighten all the time, then all you have done is added more steps and run the risk of a fast fading color,because the hair is overprocessed. Also explaining to your client, that most times, they didnt end up that dark in one shot, therefore removal should be done in a like manner, if you are going to keep the hair in good condition.