Whether you know it or not, your body will automatically take over and do things when you are attracted to someone. They may just seem like normal things to you, but start to pay attention to both you and your friends when you are attracted to someone and you will see many of the same signs in both males and females. Body language signs of attraction are very easy to spot once you know what to look for.
The smile is probably one of the most natural things to do when you like or are attracted to someone. You look at them and get caught and your usual response will be to flash a nervous smile and look away. It doesn't matter if you are a man or a woman, you see that, get over there and get in the game. That person that looked away wants nothing more than for you to get over there and start talking to them.
Another common thing for someone to do when they are attracted to someone is to preen themselves. For a woman, they will often play with their hair or quickly check their makeup as you are about to approach them. For a man, he may check his tie, tuck in his shirt or check his hair with a quick hand through it. Nothing you can do about this one, it is an automatic reflex to make sure you look your best as you are being approached.
Other body language signs of attraction are easy tell. If you are standing close to each other, the man will often try and touch the female. It is kind of a dominating 'you are mine' thing. By touching you, he is showing a sign of possession to everyone that you are now out of circulation. For the woman, she will often move closer and possibly brush legs or almost stand between your legs as a sign of giving herself up to you. Again, you can fight it all you want, but your mind knows what you want and it tells your body what to do whether you like it or not.