over the years i've learnt techniques to try and understand other people. The best thing however was when i go into Derren Brown and all the stuff he does about reading people. So when i meet someone i like, i deliberatley watch their body language to see if they like me. What's nice about this technique is that you can do it surupticiously!
The most obvious thing you can notice is what's called 'mirroring'. If you have rapport with someone, they will basically mirror your bodily movements. The best area to watch is the arms, for example if you cross your arms and a few seconds later they cross theirs-they probably like you. I usually change my arm position a few times, checking wether they do the same thing soon after.
If you are sitting next to someone, it's difficult to see if someone is mirroring you..but no worries.Check the position of their body, if they are leaning towards you they feel rapport. If they lean away-they're not so keen!
I watch body movements as, typical for AS, i have trouble looking at peoples eyes and faces, especially if i like them! It's nice as it's a easy technique to implement, that makes it easier to figure out the opposite sex! and helps to make me feel more confident.
hope this is of some use.