When your penis is fully erect, lightly enclose the glans (head) and upper shaft in your hand. Lightly rub the upper surface of the glans, and the rim where it joins the shaft, with the ball and/or base of the thumb. Lightly tease teasing your scrotum, and anywhere else you want, with your other hand. Vary the pressure and speed of your rubbing according to your excitement level and preference.
It helps to be standing. Once your penis is erect, hold your hand over the glans with your palm facing down toward it. Spread your fingers and place the ridge between your thumb and forefinger lightly over the upper rim of the glans. Then just rub backwards and forwards over the rim and the top centimeter or so of the shaft. Vary the pressure according to what increases and maintains the pleasure. With the other hand, tickle and scratch your scrotum, lightly and tantalizingly, or anywhere else you want.