How do I write my death wishes?

Hi, I am a 20 year old trying to figure out how to write my death wishes. I know you guys are gonna say I'm to young to be thinking of death but you never know what can happen. I just have a few wish like, I don't wanna be burried, I want to be cremated. Things like that. I'm not looking to write one of those things that say who gets money, house, etc. Just funeral wishes. Is it as simple as writing it or is this something that has to be done through legal?