You may want to check out Dr. Bob's educational links on the Superior website:
http://www.superiorthreads.com/education/
Is this a new problem? Have you changed to a different kind of thread? Are you using the same thread in the top and the bobbin?
Have you changed your top tension? Are you working on a domestic machine or a long-arm?
If you are sure that your bobbin tension is correct (and that is always the place to start!) and you are still seeing your top thread on the back of your quilt, it means that your top tension is too loose. You need to turn your tension dial to a larger number. If you are working on a domestic machine just turn it up 1/2 to 1 number at a time and check the back until you get the tension right.
Hope that helps.