1. His/Her Body Language Won't Lie
Suppose someone has a crush on you, it's likely that you can perceive some subtle changes because his/her spontaneous reactions tell everything. For starters, he/she can't help giving a covert glance at you more often than others. He/She may even keep staring at you but you are not aware of it. And if you catch his/her sight, he/she might well look away and pretend to look at somewhere else. Moreover, it is hard for him/her to keep eye contact with you, because he/she might stutter and his/her cheeks would flush red while talking to you. In a word, his/her body language can reveal tons of subtle information.
2. He/She Tries to Get Close to You
Another revealing sign that someone falls for you is that he/she would spare no effort to be next to you. It seems that you become a magnet to him/her. He/She may bump into you from time to time. And by getting close to you, he/she may try to have physical contact with you. Besides, he/she would borrow things from you so as to get a chance to talk with you. That said, you might think those can happen between friends or colleagues, but when someone has a crush on you, you will see him/her much more frequently than others.
3. He/She Keeps the Conversation Going
You may find the person who is interested in you will prefer to make a constant conversation with you. If he/she always looks forward to getting engaged in a conversation with you, he/she is definitely into you. What's more, your crush might well reach out to you over the phone on a regular basis. If he/she call or text you late at night or early in the morning, there is every chance that you are more than a friend to him/her.