You normally should book 2-3 weeks in advance. Try to decide your haircut prior to your appointment. Bring a photograph that illustrates the various angles. For color, they should have a book containing all of the hair dye samples.

I'll admit I have been there twice. One a great experience, the other quite the opposite. Make sure you tell the receptionist you prefer a stylist that can speak a bit of english...it makes all the difference...