If you want to impress a guy you can begin by dressing nicely to get his attention. In addition, find out the things that he enjoys most and familiarize yourself so that you can have a flowing conversation. However, in the end guys are impressed by girls who are themselves so don't overlook that matter.
Actually with me, i never try impressing a guy. They have to like me for who i am..im never going to change for a guy just to get him to like me. If you really are into him, then you can first start off by being yourself. Guys love it when a girl is themselves, being sum1 else with him is going to slowly ruin things..when he finds out who u really are then his going to start hating cuz you lied to him and not to mention to yourself. Be nice..and have fun with him. Understand jokes..if he says any or you can say it. Never go chasing him..be stuck up..make him want to talk to you. Let him chase you..as for me i love the chase..and it works everytime. Look forward to him all the time..but dont really show it..its like playing hard to get..but not too hard.