Here's a list of ways to tell if a guy is interested in a girl. And by "interested" in this case, I mean interested in a relationship, not only interested in a fling- there is a difference and guys will act differently depending on what they're looking for.
I may add more as time goes on but here are ten ways for a girl to tell if a guy is really interested.
1. He gives you gifts for no reason.
2. He doesn’t talk about other girls in front of you.
3. He describes you with words like “beautiful” instead of “sexy”.
4. He makes eye contact when you talk.
5. He is willing to go out of his way to talk or see you.
6. He asks for your number instead of just giving you his.
7. He remembers random, unimportant things that you have said.
8. He cares enough to fight with you about something.
9. He laughs at your jokes, even if they're not funny.
10. He looks for excuses to touch you (e.g. high fives, touching your shoulder, etc.)