Provera is usually given prior to clomid to cleanse the uterus, empty the old uterine lining and get ready to implantation. Clomid is a medication given to women to induce ovulation and help you get pregnant. But the lining of the uterus has to be ready for implantation, and that's why provera is often given.
Women who do not ovulate usually do not bleed regularly and the lining of their uterus grows and gets old without a period. A lining that's too thick decreases the chance of implantation and your chances getting pregnant.
In order for proper implantation to take place, the uterine lining needs to be fresh and not too thick. Provera is often given prior to Clomid to first make you bleed, to empty the uterus and clean it out in preparation for eventual implantation.
If you have not bled for a while, many doctors therefore give provera first to induce bleeding in women who have not ovulated. Once the provera has induced bleeding and cleansed the uterine lining, it is prepared for the next menstrual cycle, it is ready for clomid to induce ovulation and implantation.