Firstly I pick a color that’s not too cheap and not too expensive. I haven’t found one that I love yet but I know that you get what you pay for and if you put a $2 dye on your head you’ll get $2 results. My faves are around $7.
Secondly, spend a little time working out what colour you really want and then keep the top of the package so you don’t forget next time!
Thirdly, there’s a good reason why people use old towels and old clothes when doing it at home. I’m just sayin!