1. Be honest. Don't lie or fabricate this list. It is supposed to be sweet and personal.
2. Don't turn hates into loves. I have read some list that my friends have done for their boyfriends and they turned things that annoy them about there boyfriends into things they love. Don't do this. If you hate something that they do, don't say you love it.
4. Get to the details. This is an important one. No one wants a generic list that can apply to anyone. Pay attentions to the little things he does for you and write those.
5. Have a good time. This should be fun to write not a chore. If it starts to feel like a chore step back from the list and come back in a few days when you have fresh thoughts.
I would recommend handwriting it and not typing it out. It is more personal handwritten. Enjoy writing it and I hope he appreciates the list!