One method that has always worked for me is that once I feel like I’m approaching the PONR, I bite down on my left thumb or index finger, hard. I increase my bite force accordingly.
While biting down, I will think about some non-sex related. The key is to think about something that requires a decent amount of concentration, like mentally reciting a foreign alphabet or going through the steps of a complicated process of some kind, I.e. Cooking.
Not only does it delay my ejaculation, but it allows me to continue to thrust (lightly) while doing so.
Be careful though, I have drawn blood many times without realizing it until afterward. It’s not so bad though, as I will usually turn it into a compliment: “OMG baby, you felt so amazing, look at what I had to do to keep myself from cumming!”
Not the safest or most effective method, but it has always worked well for me.
You should definitely work your PC muscle and read up on the link that Dymn provided. These will provide you with more effective and safe methods for delaying ejaculation, as well as contributing to overall penile health.