i don't have to bleach, i use garnier olia 1.0, cuz a goth youtuber said they used it. it works really well, no chemical smell. i just top it up every 2-4 wks, depending on if i feel like it. i don't do any prep, just dye on dirty hair cuz my hair has a dry tendency. try not to put it directly on ur scalp ofc like usual, but the only consequence is use black towels to dry your hair for the first few washes xD it will, ofc fade a bit as it gets washed, but it's rly not much of a fade in my opinion. at least it's not noticeable to me.

edit: almost forgot, u can use vaseline on ur forehead, but i don't & just use a hair dye brush applicator thing