To generally make your orgasms longer and stronger you need to regularly start doing exercises known as Kegels. This are done by clenching and relaxing the Pubococcygeus muscle (PC muscle), which you will be able to locate by stopping urination mid-flow. The muscle you use to do this is the PC muscle. Now that you know what it feels like, I recommend that you practice exercise this muscle, by clenching, relaxing and then pushing out about 100 times a day. You will definitely notice the results in a short time.
The PC muscle can be strengthened with duotone balls, which are two hard plastic balls with a smaller solid one inside. The balls are tied together with a cord. When you place them inside the vagina the heavier balls rock when you move, encouraging you to clench and relax your PC muscle. Doing house work will never be the same again! An added bonus is that they are wonderful with clitoral stimulation. You can ask your partner to stimulate your clitoris and as you are about to orgasm have them pull out the balls. This stimulates the G-Spot and can give you a wonderful orgasm. Small vibrating eggs can also be used internally to strengthen the PC muscle and are lots of fun. If the eggs are not latex covered you will need to use a condom, because any liquid travelling down the cord will effect them. You can also use them externally on the clitoris and as they are so small they are portable and make a great travelling companion.