In earlier years, stroking was all I needed to cum. As I aged, I needed more stimulation to have strong orgasms. This is a sure-work technique for me:
a) I watch porn movies, while stimulating (with my fingers and vibrator) my penis and nipples and anus on and off. This could last more than 30 minutes (just don't over do the stimulation or you will cum too early).
b) When I am 'ready' (lots of pre-cum on my fingers from the dick-I lick off the clear pre-cum, too) and when my favorite part of the scene is playing, I stick a lubed plastic tube (small diameter to suit you and make sure the other end of the tube has a cap that is bigger than the asshole so it won't get lost in the ass!) into my ass while keeping the vibrator at the asshole.
c) I then caress my balls with fingers and stroke my dick with the other hand. I continue to do this till I'm about to cum then I stop stimulating (depending on where the over sensation is-the anus or the balls or the penis-for me usually it's the anus because of the vibe.)
d) I then repeat c one time or twice before I can hold no more and then cover my dick with a cloth that's rough in textile and keep stroking the dick as fast as I can (while keeping the stimulation at the anus and the balls-the vibration through the tube helps build up the pleasure feeling) and boomm, I'll have one of the strongest orgasms.
It's important that you do this undisturbed or else you'll want to cum quickly. A typical session for me is over an hour. Also try different kinds of cloths till you find the right one and stick with it.