Don't be disappointed with yourself, as it may take several sessions before you can relax enough to really let go. When you feel a gathering tension in the vaginal area and a build-up of warmth, orgasm is on the way. Continue to stimulate yourself, as if you stop, these sensations will fade and it may be difficult to get them back again. The clitoris becomes increasingly sensitive as you proceed, whether you are stimulating it directly or not, and then orgasm breaks out with waves of vaginal contractions. Some like to insert a finger into the vagina as they come.
Most men are expert at giving themselves pleasure, but there's no harm in extra practice.
A good way of finding out exactly how your genitals respond to stimulation is by soaping and gentle massage in the bath, allowing yourself to fantasize as you do so. Some men enjoy fondling their testicles, and some enjoy penetrating the anus with a finger. There are many different strokes you can use on the penis. Then you can let your hand glide up and down the shaft in long slow movements, gradually building up speed and pressure. You may enjoy rubbing or tickling the glans of the penis, though for some men this is too sensitive.