Find out his turn ons..usually some sensual kissing works
Go on a date to somewhere romantic and get him in the mood of it.
Just tell him straight.
It means he is trying to fit in.
Ask him where he is and would he be more comfortable in bed?
tell him when hes in a good mood
She is all happy and not cranky and she is in a good mood and she starts sucking up to people that she never did before.
just say, "I want you" and straddle him :p
Try to break the news to him calmly when hes in a very good mood.
For sex just say you are not in the right mood but for being her boyfriend just say you are not ready for that type of relationship.
Just one day when he is in a good mood tell him you need to tell him something important and then tell him.
It all depends on how he feels about you.
Pretty simple really.just get him in a good mood(however you think best)and tell him.That simple.