Legal Question in Criminal Law in California

By showing with admissible evidence and testimony that a serious error or negligence was committed by counsel, and that the trial's outcome would have been different/better 'but for' that error. Error could be failure to introduce some evidence or failure to prevent some evidence from being introduced. If you entered a plea bargain, you likely waived any such claims. Discuss your claims with experienced appellate attorney, whom you will need to present your appeal.