Couple things. Id recommend going to Sally Beauty and having them hook you up with the right bleach, toners, etc for your hair type and color. You're gonna be doing a little damage, regardless, but waay more with box dyes. Don't forget to get some professional conditioner cause yeah, gonna want that.
Second, be prepared to do this again. If you're naturally a reaally dark brunette, your hair will probably come out a darker blonde the first time. Wait 6-8 weeks or so and do it again, and it should come blonder. But waittt to bleach again if you don't like the color. Your hair needs time to repair

Also, roots are a pain. One of the reasons I didn't keep up with it. I get at least 3/4 inch new growth a month, so my roots come through fast. Just remember, it's a committment.
Also? Don't dye the eyebrows. Please, please, pleaasedont try that. If your final goal is platinum get the eyebrows done at a salon.
Other than that? Have funn! I've done black, golden brown, platinum blonde, and most recently red. It's funn to mix things up, so enjoy. Lana is a goddess. And enjoy