#4) When you do start, start slowly. Slowly take his head into your mouth, just the head, and listen to his reaction; I promise, you will get a very good/pleased reaction. Make a note of this reaction; this is probably what he will almost always do when he's pleased. Personally, my guy sighs and moans a little, and it is the best sound in the world to me. Your guy might do the same, he might gasp, he might jerk his hips, he might grab your hair; whatever he does, he is showing you pleasure and you need to pay attention to that. Slowly work your way down further and further. Not too fast, because you need to condition your body to this new and wierd activity. Stuff is supposed to go in your mouth then down your throat, not in and out, so you will feel wierd. Don't feel pressured to "deap-throat" it because you will gag and lose all desire to give head.
#5) When you start to feel comfortable, then change it up. There is nothing more boring to a guy than just straight up, down, up, down, etc. etc. etc., especially for a guy who has had a blowjob before. Just like when you masturbate; you don't just do the same exact motion until you cum, do you? You change your technique, you try new things, and you do this often. I have been giving the same guy head for two years, and he still loves it because I still change it up. Try flicking your tongue under his shaft. Swirl the head around with your tongue. Rotate your head. Start pumping the base half while giving head to the top half. Change your rhythm. Go slower, quicker, tighten your lips to add friction, flatten your tongue around the sensitive spot underneath the head. Play with his balls. P.S. Two VERY important notes here: Number One, be careful of your teeth; they hurt. Always pay attention to where your teeth are on his member. Number Two, do not play rough with his balls, if you decide to go there. Be very gentle, almost ticklish, and pay attention to grimacing/frowning/anything to show he is not happy. His balls are the most fragile spot and are not meant to be grabbed roughly or jerked around. They are meant for light sucking and licking, and light cupping and massaging. Some guys don't like any attention around their balls at all, so pay attention.
#6) Get ready for the finale. Have a plan beforehand what you intend to do here. Are you going to let him cum in your mouth? Somewhere on your body? In a cup? Are you going to swallow? I would suggest that, for your first time, either jack him off at the very end or let him cum somewhere on your body; face, chest, stomach, hair, whatever. Cum washes off, so don't get picky about it; let him go where he wants to go, if you decide to go this way. Head is all about pleasuring him, so give him a choice. However, do not let him cum in your mouth unless you are totally ready. When my guy came in my mouth for the first time, I gagged; I was SO not expecting the taste, and nothing is like it if you haven't tasted it before. So, if you let him cum in your mouth, have a cup ready, be ready to rush to the sink, ready to spit it out your car window, whatever; just be ready. And do not swallow it unless you really really want to or really really want to turn him on. To this day, I get stomachaches when I swallow my guy's cum, but I do it becuase it turns him on. Just remember that this is about him, not you.
Ok, so here is a summary: be sure you're ready, don't expect to give flawless head the first time, get in the mood first, start slow and work your way up, give him variety, and have a plan for what you will do when he cums.
Always, always, always make sure that you do what you are comfortable with and don't feel pressured. Also remember that he is a guy and any attention his penis gets is gonna feel great, especially the first time. So don't worry; there's nothing to be afraid of or get insecure about. And if he is the kind of great guy that deserves to be getting head, then remember that, even if you're horrible the first time, he is going to love it. ;)