Cleanliness a given for the both of us (fresh sweat is a turn on to me, but as a rule, you should be exceptionally clean in the genital area, behind the ears, clean hair (trust me, hair smells greasy and stale after a few days of no washing), armpits and fresh and clean mouth), then :
Before: Sexual tension. Not too much. Not overt. Not too confident. But must exist. Can be summed up as an appetite for me and my body with eye contact. An instant turn off is baby-talk, complaining about life, whining, any expression of boredom in life. Make sure all that ends way before sex. So if you are having dinner/date with someone new or sofa cuddling with a long-term lover, do your best to make the hours leading up to sex have a positive feel, so that sexual tension can build.
*During: *The number one turn on for me is lack of inhibition. This doesn't mean doing a million positions under the sun, it means being able to enjoy vanilla sex with abandon and appreciation. Being comfortable with yourself in your own skin, and with me. I will feel comfortable with you, and enjoy your body no matter how much of a tummy you have or flabby your arms are or how much butt hair you have, if i feel that YOU feel comfortable with yourself, and very appreciative, and grateful for the shared experience with my body and all it's flaws. You can show me this by kissing my thighs and my breasts, no matter how large/small/stretch-marked/imperfect they may be. By showing with natural sound and touch that you love my shape/smell/style. An example of this not showing is someone who doesn't like or enjoy or feel confident in licking pussy. If you enjoy it, it shows, i feel comfortable. If you are awkward touching me, or make any single even in jest joke about my body at all, it will ruin it for me. Don't comment on how flat my tits are, or how uneven my labia is, or how all your other girlfriend had really pert asses — even in passing. This is not the time or the place. I will just dislike you more than feel insecure, and then what's the point of sex.
After: Don't be an asshole. Cuddle me at least a little, unless i feel liek i need some space. In that case, simply reaching out your hand to touch me in some way is nice. Tell me how good it was (if it was). Tell me how much you love my ass/pussy/way i moan/ feet... whatever. Give me a small genuine compliment. The rest depends on what you want out of the relationship. I personally think that even friends with benefits and fuck buddy situations work best when there is genuine fondness and respect... so nuture those