Step one, don't have a very small penis to do it on...

You don't need to use your whole fist - thumb and forefinger will do - and the 'away hand' can also pay some attention to their balls. Similarly, it needn't go past the head into your mouth.

Also, ask him how he would like it. Tell him you are not sure as you haven't done it before - it'll probably make him feel special. 

I second just include him and ask him what he'd like. It helps if you have small hands because it makes them feel bigger probably lol. I usually have one hand on the shaft and the other massaging the balls while I work on the tip and then maybe change things up with two hands on the shaft and some licking just generally you don't want to keep doing the same thing if you surprise them every once in a while by doing something different with your hands and tongue they tend to like it.