Wrap one hand around the base of the penis. That way you control how deep you insert the penis into your mouth. Otherwise a sudden thrust may block your throat, causing a rather unpleasant gag reflex.
The most important actions are sucking and licking the penis. Concentrate on the most sensitive areas of the penis.
Don’t be afraid to slobber; saliva is a natural lubricant. Coat your lips and tongue with extra saliva. You could start with a long very wet lick from his balls to the head of his penis. 
Cover your teeth by your lips. Most guys don’t like the scraping.

.