well... i think when you do highlights, its important to remember to NOT start making highlights at the top layer where you part your hair. you want to start under a small layer at where you part your hair.
and if you make booboos, it is important to carefully wash it off or else you'll have blotches...
and get someone to help you cuz its hard to see the back of your head
if you want whiter hair, use foil and sit near a heater. heat is a catalyst for the bleach to react faster. you might even have to bleach twice is you are going from black to platinum blonde
do not rub into your scalp..
hope that helps!