I can't answer about ruining. I enjoy edging though. I've edged from a couple hours to 3 days. It took a little practice but I just keep going till I think I'm about to cum then stop everything. Don't touch, hold anything with your dick. Most importantly, switch your thoughts to something else. Give yourself a few minutes to several minutes to recover and repeat. The longer I edge, the more intense the orgasm I have when I finally cum!!

It takes a bit of practice and knowing your body. I've managed to cum like 6 times before from doing it. Personally I find it much easier to do when standing up as opposed to sitting or lying down, and also when I've already cum within the past 2 or so days. When I haven't orgasmed in a longer period of time, I find it more difficult to get the timing right. Although you will get bigger spurts of cum if you can pull it off that way.

What I have read that helps with stamina and edging it to play up and down starting low (far away from cumming) before moving up. So if 100% is hitting the threshold of orgasmic inevitably you don't start edging close to it. So you go up to 30% before stopping and letting yourself calm back down. You then work up closer to 50% before letting yourself calm back down. Then move to 60% before calming back down. You then go 70%, 75%, 80% until you get as close as possible to the edge.

A lot of this comes from Urban Tantra which has a section of erotic massages for penis havers which suggests the same idea.

What others said + edging is the quite easy part for me, yet sometimes I cum seconds before the edge. Ruined was never my best, so I never do it.