It is difficult to answer this without more facts, but, in general, successive Writ Petitions will be denied. In my experience, trial counsel can make a Motion for a New Trial after conviction and prior to sentencing. If this MNT is denied, you can include it in the Appeal which would be filed within the 60-day time limit. Assuming that you did not file an Appeal, or that it was denied, and that you have already filed one Writ of Habeas Corpus which was denied, I think you need to file the Writ with the next higher court, which sounds like the California Court of Appeal. You should contact the Attorney who did the first Writ, whether private or Appointed by CCAP and see what they say.
I agree with my colleagues. It is highly advised that you consult with an attorney that is experienced in this area. As stated previously the facts of your case is imperative to determine what other mechanism is available to you.