First what you can look for is body posture. What is the his body posture when you are talking to him or are in the same room as him? If his body tends to face you, it means that you are valuable to him somehow. Doesn't necessarily mean that he likes you; it just means that you mean something to him.
Next is his eyes. Do you catch him looking at you often? Does he make a lot of eye contact with you? Those could be sign. But like with all signs, there are no guarantees. There are some guys who just like making eye contact to whomever he speaks to (I know someone like this), so you never know for sure. But usually, those are good signs.
And finally just see how he behaves around you and treats you. Does his behavior change when you're around? Is he nicer around you than he with most people? For this one it can be a little tricky to know because every guy is different in this aspect. You'll just have to use your intuition on this one.
I hope some of this helps a little.
