I think you can usually get a baseline on how good someone will be in bed by how they give you a massage.
Don't get me wrong, here - it's not a foolproof system. Massages won't tell you if your potential partner's anorgasmic, or if they're disgusted by oral sex, or if they freeze up whenever an intimacy barrier gets passed. But the way someone touches your skin gives you valuable data points about their sensitivity.
A brief temple massage or neckrub can give you valuable clues:
- You can see whether they know where to touch you. Not everyone likes being touched in the same areas, of course... But if someone knows the right muscles to squeeze on your back, they usually know the right muscles to squeeze elsewhere.
- You can see how bold they are about it. Some people are terrified to be in human contact, and that terror usually transfers to the boudoir. If they're skittish about rubbing your neck, chances are good you're going to have to be more aggressive in bed (which may or may not suit your needs).
- You can see how heavy their touch is. Some people touch very gently, giving you butterfly kisses with their hands; others bear right into you, tearing flesh from bone. (This is the least accurate impression, however, as some people have been trained in a massage technique. I've been surprised. However, most of the flesh-tearing women went on to lever my penis like it was a gearshift and they were desperate to win the Indy 500.)
- You can see how sensual it is. Some of the massage therapists I've known have discussed how they have to dial down their sexuality for massages; some people just have a touch that imparts a certain erotic charge which can be embarrassing in professional situations. If you're willing to lay back and explore (which isn't always doable, especially if it's in a room full of people), you can see whether there's that spark.
- And most importantly, you can see whether they react to your reaction. There are people who have A Massage that they give, and you're going to get it whether you're enjoying it or not. But the most important carnal skill is the ability to read your partner and improvise on the fly. If the person who's giving you a backrub notices your discomfort and changes approaches, if they shift areas to make sure no one part becomes oversaturated, if they bear down a little more... Then you've probably struck gold.
In a pinch, you can sometimes read into it from the body contact provided by a hug, but that's a lot more difficult (and a lot creepier, depending on the nature of the hug).
I'm not saying that every backrub should be a testing zone for a new lover, of course; sometimes, a backrub is just a backrub. Nor are these clues infallible. But I'm saying that if you're in the market for a new bed-buddy, you can frequently use the warmups to see if they're worth pursuing the rest of the way.