This is something that's been bugging be for some time. I'm totally clueless when it comes to hitting on a guy. My "gaydar" is pretty good, but I never am able to do anything besides walk around or blush. Ugh. I hope someone else gets some help out of this. Maybe I'm just under the influence of sleep deprivation. It's 4:00 a.m. for me.
Compliment them. Smile a lot. Eye contact is key. Physical proximity is always nice. If they're the touchy feely type then you be the same. And I must repeat, eye contact is key.
Don't be fake. But, make eye contact, smile a lot, compliments on features like eyes, smile, hair. If he is wearing a shirt with something you like say something. Try side comments too. At one of jobs there was a cute girl that was leaving for a month. When she told me I said, "That's a shame it's going to be a lot less pretty around here."
In a sense flirting is like a dance; meaning if both partners can pick up and stay with the beat, it works. If one of you is on a totally different page then it would probably be very embarrassing. Start off slowly, with a compliment for example and dabble with light conversation. Then if you feel it is okay, proceed to phase 2 which includes light touching on the arms/hands etc. Always keep your eyes on their's, and be yourself at all times. Just go with the flow, and do whatever seems right at the time.
smile cheekily and keep eye contact. a light smattering of flattery helps, but don't go too overboard! some people find it irresistable when a guy bites their lip (i'm a sucker for it), but don't do it so much that you get sore or look too nervous. it's about balance really, but ultimately you need to be yourself. be confident in your pull-ability and it's like moths to a flame!
Be subtle. "I'd like to kiss your face" never worked for me... Wink occasionally, but never after you say that you dislike something, unless you actually like it.