The old saying... "the eyes are the window to the soul", is 100% true.
The eyes DO reveal a lot about what a person is thinking.
If you want to know if a guy is interested in you, then understanding the body language of eye contact is the first place
to start...
Direct eye contact is better than flickering movements towards and away from you, but both can denote positive feelings towards
you. Direct and lingering eye contact will usually mean that he wants to get to know you that little bit better. Flickering
glances will often mean this too, but will also show that he is shy and reluctant to make the first move.
However, if the man in question studiously avoids meeting your eye or glares at you then the likelihood is that he is not
taking kindly to your presence. It may be that he has already formed an opinion about you that is negative, that he is unavailable
for another reason or simply that he just does not want to talk to you.
If you are up close, look carefully at the man's eyes, and see if his pupils are dilated. If they are- it's a sign that he
is aroused by you. This is totally subconcious, but is an easy thing to check for. The more wide the pupils, the more the
man is attracted to you.
Eye contact is a good way of judging whether or not you are getting a positive or negative response from your man, but like
all body language, should not be used in isolation.
You need to check all of his body language to get a true sense of what he is thinking.
His hand gestures, general demeanour, his facial expressions (Ideally he should be smiling during the eye contact), are all
important too, and as you learn more about body language, you will find reading men easier and easier.
But while your starting, the eyes are a great place to start, and should give you a good idea about what the man in question
thinks about you.
Good luck!