Make sure you prepare your hair before bleaching it. I recommend doing a deep-conditioning 2 weeks before bleaching it. The bleach is really harsh on your hair. It basically gets into your hair follicule and rips the color off. If you skip this step you may end with dry and damaged hair.

If you start this process with dark color and want to get that ashy light blonde hair DON'T expect to achieve it for one day. Stripping that much color from the hair may take a few times. Also, make sure to give your hair a break between treatments. 

Okay, unless you have some experience in this whole bleach process, don't, I REPEAT- DON'T do it by yourself. You may end with brassy hair, or even ugly strippy hair color. Believe me - it is much more cheaper to go to hair salon and let a professional do it. This whole process may look easy, but it's not.

I am so sorry to say it but your hair is going to become dry at some point. You will have to limit the amount of heat you are using. If you don't take care of it properly it is going to become worse with every root recoloring you are doing. Bleached hair needs more care than dyed hair. 

Your purple shampoo is going to be your next bestfriend. I used to have silver hair a few months ago, which was so hard to maintain. Purple shampoo tones your brassy strands to a nice matte cool-toned color. I couldn't imagine living without purple shampoo back then!

6. Be careful if you want to go back to your darker color

Unless you have a dark blonde hair color, you have to be really careful here. Light blondes don't have any warm undertones, which basically means that if you try to darken your hair it's going to turn green. Been there, done that. Easiest way to get back to your darker hair color is to apply toner with red tones in it. That way the red undertones in the toner are canceling the green undertones in your hair and help you achieve your desired color.