Here is a short list of things to avoid if you only want to be friends with someone:

1. Don't have sex with them
2. Don't introduce them to the "3 most important people" in your life (grandma, mom, best friend)
3. Don't tell them, "I've never felt this way about anyone before" repeatedly
4. Don't spend nights on end with them, cuddling with them, your head on their chest.
5. Don't become upset when, after failing to avoid 1-4, they are unsure if they can just be friends.

Just a suggestion.