Started doing this a few years ago and am pretty good at it. Once rode an edge for nearly an hour.

Three things:

1. Stick to the shaft. The tip of your penis and the areas close to it are waaay more sensitive than the rest. It'll take longer to reach the edge but it'll be less likely for you to go over
2. Don't use your whole hand. I start with my thumb, index,and middle finger going up and down. After you hit the edge, just stroke the bottom up and down with only 2 fingers. After a few minutes on the edge, bring it down to 1. I usually switch between 1 and 2 a lot as I get further from and closer to orgasming.
3. Don't be afraid to let go and cool down for 5 seconds. If you get scarily close, get your hand off, and (if you're afraid you'll still go over) do something to distract youraelf from the pleasure. I tend to twist my own nipple or smack myself in the balls. Has saved me countless times.