Suck, don't blow. But I think the most important part is keeping your tongue firmly against the underside of his penis. The underside of his penis head is the most sensitive part. Also remember to breathe through your nose and not your mouth.
You can put one hand around the part of his penis that's not in your mouth and stroke it while you're going up and down. He'll like that. But don't keep him in your mouth the entire time or your jaw might start aching. Maybe start him off with stroking with your hand and licking with your tongue. You can also do that in between.
Be careful not to scrape him with your teeth while you are moving him in and out of your mouth. Some guys do like to have their head nibbled on very gently though.
Keeping him in your mouth when he cums and swallowing it will probably turn him on most, but do whatever you're comfortable with.