Eye Contact and Smiles
If a boy is interested in you, you'll find that his stare is drawn back to you, even if you are in a crowded room. He will make eye contact with you to let you know that he's interested. He will also offer a friendly smile to show that he finds you attractive. By smiling and making direct eye contact, he's using non-verbal cues to let you know that he's interested in getting to know you better.
If a guy comes into your personal space, he is showing his interest and indicating that he wants to get closer to you. When you talk, he may lean in closer to you or incline his head toward you. Physically, he is showing that he wants to be closer because he is attracted to you.
When you talk with him, his conversation will be key in determining if he is flirting with you. If he listens attentively, smiles at your jokes and asks appropriate questions while you are talking, he is interested in you. If he quickly backs away or crosses his arms, his withdrawal will be a clear indication that he isn't flirting. He may also offer compliments to you. He may say that he likes your hair or your eyes. Compliments are very obvious signs of flirtation.
During your conversation, he may lean close and put his hand on your arm or your shoulder. Light, casual touches are flirtatious and show his attraction to you. If you are standing in a crowd, he may move closer so that his body can brush against yours. With this movement, he is showing others that you are together. Physical touches can be a strong indication of a boy's interest.