Love has its own Body Language

Focus
If you’re interested in someone, you focus and pay attention. If you’re not interested in someone, your attention wanders. So if you’re sitting with the person you like, and he/she is looking at you when you’re talking, that’s a great sign. The eyes have it all and thus if the person is not interested he/she will keep looking out the window, or watching other girls/men.
Dilated eyes
As they say “The eyes are the window to the soul.” Thus while you are talking to the person you like, your eye pupils dialate (get bigger) when you’re excited. So if someone’s eyes look really big, it shows they’re interested. Thus keep your eyes on him/her and observe the eyes.
Lip and Mouth Activities
A girl might bite her lip gently, or run her tongue along her lip to show that she is interested. Some girls even do this deliberately to flirt, although it rarely looks natural. If you’re a girl, don’t try it, unless you’re really sure it looks natural.
Hair
Fiddling and playing with hair is one way to show that you are interested. Girls wrap their fingers in their hair. Guys run their hands through their hair. Note that twirling your hair is more a sign of boredom and distraction.
Arms and Hands
If the girl keeps her arms or hands closed or crossed (which is normal if its cold) then that is a clear indication that she’s not feeling comfortable. Arms that are out and away from her are less ‘defensive’. Also, if the woman leaves her wrist-up, it’s sort of an “I trust you” motion.
Legs
Women normally like to sit cross-legged and note that it doesn’t mean that she isn’t interested. So forget about that and concentrate on the toes because, toes tend to react to general body energy. So if someone’s feeling bored and listless, they might just lay there. But if someone is feeling excited and energetic, the toe might make little circles or bounce. Women when are interested point their toes towards the man.
The Voice
The way someone talks and especially the tone of the voice is hugely important. It will instantly tell you whether: Are they bored and weary? Are they thoughtful and quiet? Are they enthused and interested? To find out whether the person is interested in you first watch your own speech and then watch how their speech changes. If someone wants to ‘get along’ with someone else, they naturally match their speech patterns together. If you’re interested in someone, you start to naturally speak like them, using the same tone of voice, the same loudness/softness and speed, the same phrases even.