If you don't know what your "trouble area" is, take about 15 minutes to find it...
Try to relax your body as much as possible while you lie on the massage ball with different parts of your body. You'll find one area that is unusually tight (and probably the most sensitive, too). Remember to chase the area with the most tension, not necessarily the most pain. A healthy, relaxed muscle will wrap around the ball to some degree. If you feel that you lie on the ball with one particular area and your muscle mass simply does not give at all, THAT is your spot!
Once you know your "trouble area," work it for as much time as it takes to get a significant release in that area. If the tight spot is in your center thigh or between your shoulder blades (where everyone has a significant amount of muscle mass), when the muscle "gives" and you get that release you should feel the ball sink into your flesh as your body absorbs the ball and it is FAR more comfortable to lie on it.
Post your comments regarding how easy it is to find your tightest muscle, and how long it takes to let go.