I know you've seen a billion of them on here; "How To Give A Guy Great Head," "How To Please Him," etc. I thought I would add my two cents because there are some things I haven't seen on here, plus I absolutely love giving my guy head, so my advice will probably be pretty awesome.
#1) Make sure you are both ready. There is nothing more horrible than saying you're going to give a guy head and then not following through with it; trust me, I know from experience. So, before your first time, make sure you are absolutely, 100% okay with it. If you and your guy have been having sex or have been "active" then the tips are going to be different than someone who hasn't done anything with the guy they're trying to please. For a couple who have been active and are comfortable with each other, head will come easier; you already know the other's reactions, their tendancies, etc. So, the main thing you have to remember is that, no matter what you do, ithe ending won't be some horror story; you'll just have to keep doing it until you get it right, which is half the fun. However, for a couple who have just met or are just starting their intimacy, you have to learn the signs, and this "How-To" guide is specifically for you. So anyway, make sure you're ready.
#2) Don't expect too much the first time. Few women are experts at it their first time around, and most are still getting over how disgusted or awkward they feel. Feel free to explain this to your guy; honesty works wonders. Let him know that you're nervous, but don't worry him and don't make him feel like he's forcing you to give him head. Huge turn-off. It won't be horrible, because guys just like attention down there and anything they can get, they love (usually).