There's many ways. One of the big things I use is eye contact. Most people drop their eyes when their eyes meet someone elses but when your "caught" looking at the one you like it's prime time to keep looking into their eyes, flash a smile, blush THEN drop your eyes. But always look back at them and continue making eye contact and keep flashing smiles.
That's just one thing I do. I use a whole list of things though. Everything from eye contact, smiles, batting eyes, and even a little physical contact. Use what your comfortable with.
first make sure he and u feel comfortable around each other anf flirt
how 2 flirt :
1. fluter your eylashes
2.be confedent
3.put ur hand on his knee
4.ask for him for a day u can study that way he is away from his friends and you can have alone time
5.be your self
that sshould do the trick hun if that dont work then god knows what will
*eye contact is the best thing
*touch them by "accident" is also good cause
*smlie at every chance you get
*make your self stand out (not horrible stand out, but a good stand out)so he'll notice you more