There are quite a few techniques and the simplest one is to keep your eyes open. Kegels always work for me, but you have to squeeze really hard and hold it as long as you can. To do them properly you need to exercise the PC muscle every day.
Tantric sex is partly about sexual energy re-circulation. As you get aroused you imagine the sexual energy being drawn from your genitals, up through your spine and away. When kissing during sex, you pass this energy to your partner. This one is probably easier said than done, and knowing meditation also helps getting into the zone to make it work.
I know your problem as I have a 6" girth and I've had sex with some Asian girls who were amazingly tight. The most recent I was on top and no matter how hard I tried I immediately went into borderline coming. I knelt between her legs and fucked her really, really slowly, which was a position that massaged her g-spot. After a while she forgot about the slow thrusting and started to head towards her own orgasm instead. When she came I came, but we'd been at it for a good while before that happened.