Confidence is attractive to most people. My advice is the following, you both like each other, just tell him/her!
"Hi, I think I like you."
or if I didn't think I was talking to a young person,
"Hi, would you like a drink?"
Even if it turns out they do not like you, the worst you will get is a "no". And take it from someone who has had may of those- You will survive!
If you make the first move, and they like you, all will be fine.
If you are over 18/21 depending on your country, a little dutch courage does not go amiss!