How do you be really good friends with a guy?

Alot of people say that you must be yourself which I believe is not at all wrong.If you just want to be friends nothing more nothing less,show him the side you would show to your best friend. Be open with him and show him that you have nothing to hide at all. That way you're making him aware of all your intentions.Even if you have something you're hiding from him, he'll never know as long as you give him that impression.