One of the best ways to do this, when you already have a average size penis, is through penis extensions or vibrating cockrings. Cock rings or penis rings, can stimulate both the clitoris as well as the G-spot. Other ways include sex toys and lubricants designed to stimulate the vagina. Our recommendation would be a product like the HotGVibe Vibrating Cock Ring, it is a clitoral and Gspot stimulator.