Do boys really care about the girls body?

Yes, they care. Just stay lean mostly though, maybe do some sit-ups, but don't get too defined. And as for sex tips, I don't know. I heard that a lot of girls ignore a man's testicles during sex, and that it is a turn on to roll and caress his balls in your hand while you have sex. Also, you could heat things up by doing it in different places, like the shower or something.