This page has great meditations for the aura. http://www.angelfire.com/empire/serpent ... ation.html
A basic one would be to breath or draw in powerful white/gold light into your aura. You also want to do a this for your aura of protection as well. A powerful method is to go outside and use the sun. Just bring in the suns energy, the sun is a wonderful way to clean your aura as well.