If a lot of times you look up, and he’s looking at you, that’s a good sign. It means that he likes looking at you, but he might be too shy to make his interest known or to approach you!
If he moves to get closer to you, this is also a good sign. For example: if the two of you are walking together and his arm keeps brushing up against yours. This can be a subtle, mostly subconscious movement, or it can be much less subtle. You can use a bit of moving closer of your own to flirt with him. For example, you might walk around a puddle on his side of the puddle so that you get closer to him.
For example: he takes a sip of his drink a few moments after you do. Or he rests his arms on the table when you do. You can use this to flirt with him, as well. Mirror some of his movements. If he crosses his legs, cross yours. When he takes a sip of his drink, wait a few moments and then take a sip of yours.
Some ambiguous touching might be: hands brushing when you’re walking together (could be on purpose, could be accidental), patting you on the back (this seems more a friends type touch), anything “guy-ish” (like fist-bumps, high fives, and the like). Touches that are more likely to designate interest: he puts his hand or arm on the small of your back to guide you, when he hugs you the hug lingers (he may brush his hand down your back or along your side), he puts his arm around you. You can use touch to flirt back with him. Put your hand on his arm when you’re talking to him. Nudge him when you say something funny (and grin at him).
If he remembers what you tell him, that is one of the best signs. That means that not only was he listening to what you were saying, that he cared enough to remember it. If he’s only in it for sex or for his own ego, he might pretend like he’s listening, but he probably won’t actually be listening. Make sure that you listen to him as well. He’ll love that you’re interested in him and that you remember what he says to you. It’ll show that you think he’s important.
Look for things like unexplained laughter, sweaty palms, or fidgeting but if he’s keeping you in the friend zone, then don’t bother with him. He might have a little difficulty maintaining eye contact with you without becoming a little uncomfortable. Do your best to make him comfortable. Tell him about that time you spilled a drink all over yourself at your work party, or something to make you seem human and not inhumanly awesome.
He might do something like lend you his jacket when you’re cold, or he might offer to buy your coffee drink even though you aren’t dating, or he might offer to drive you to the airport when you have to catch a flight. Do nice things back to him. This way he’ll see that you are someone who doesn’t take other people for granted and that you notice and appreciate what it is that he’s doing. If you aren’t interested in him try not to take advantage of his interest in you.
He might compliment you on a new haircut (which means that he’s been paying attention), or tell you that you’re doing an awesome job on that project for school.
He’s also unlikely to ask you any questions about yourself. This is a guy you definitely want to stay away from. Either he’s not interested, or he is interested, but he’s too much of a narcissist to really see you as a fully fledged person who’s interesting in their own right.
A big warning sign for someone like this is if he’s too busy checking his phone to listen to you. It means that he’s more interested in other people than he is in you.
He never tries to get closer to you, or touch you, even subtly. If he doesn’t do particularly nice things for you, or anything for you, this could be a sign that he’s not interested. Again, even if a guy is shy or dealing with his interest by ignoring you, he’s still going to want to be around you. If the guy is never around, well, that’s a sign he’s not interested.
This is also true if he avoids introducing you to his friends. It shows that he’s not very serious about you, because otherwise he’d be dying to show you off to his buddies.
