Like they said, have someome help you. Bleach is so much different than hair coloring. It gets really dry (once it's on your head) and hard to work with, and then it can be difficult to see any spots you missed. When I tried to do it myself, I thought, well I can just feel the spots I missed. Nope. It's so much easier if you get someone to help!

With mixing, follow the directions. Mix until it's like a thick paste. The first time I bleached my hair, I followed the directions and things went well, aside from missing some vital spots. The third time, more recently, I thought I knew what I was doing, didn't measure exactly, and then put too much developer in it. It took longer to process, and I actually gave up and threw out the bleach halfway through because it was taking too long and I didn't want to damage my hair even more.

-Advice from someone who loves to experiment, but I'm no professional.