How to get comfortable with sexuality?

i am 16 and have only had a couple boyfriends, i m not usually comfortable with sexual acts and get really nervous and feel like i cant be sexy. my question is how to get comfortable with myself and how to experience sexual acts with out being a total loser at it. i tend to fall for guys who have had sex before and i dont want to seem bad and not sexy.. so how do i get comfortable with myself enough to start having sex with guys.?