Be yourself and be confident about who you are. Nothing impresses more than someone who is genuine and not fake. Be confident in who you are, your opinions, your taste, etc. Just be true to you and you will shine. And, don't forget to smile! Good luck :)
One of the best ways to impress someone you like is by maintaining confidence and at the same time being true. This is both for yourself and the friends around you. Be friendly to him or her and show some general interest but it has to be natural.