The best thing to a guy is when a girl is really into it. Meaning she's not just laying there having him do all the work. Trying different positions in which the girl does some of the work. Initiating foreplay, letting him know what it is you want him to do to you.
do you mean first time with him or in general? if second then relax, foreplay is very important and having sex the first time is the same as with every thing you do the first time. you need to get experienced and I'm not sure if you will be able to impress him...
I don't think you should be too eager to impress him, especially on ur first time. The only advice I can really give is just tell him that he can do anything he wants with you and have you in any way he wants... That would probably work, lol.
If this is your first time, don't have high expectations. He should understand that you are a virgin and know to go slowly to avoid hurting you. If you are mainly concerned about impressing him, maybe the two of you are not emotionally ready for sex? Another thing--your inexperience may be more of a turn-on to him than any "impressive" moves you might try to fake. Relax, use a good lube, and figure things out for yourself--it's the best way.
Foreplay is the key. My boyfriend loves it when I come one to him. You should be the one to start it. I can't vouch for every other guy out there, but my boyfriend loves when I give him oral. He says its his favorite part. It arouses me too. Oh, and guys love a girl who talks dirty.