General reasons for appeal are an unfair trial--often juror misconduct claims, violation of constitutional rights, errors in rulings by the court or incorrect application of the law by the court, defense lawyer ineffectiveness, and insufficient evidence. Just about every criminal found guilty in the US has a right to appeal. Some (wealthy) defendants will have an appeal attorney as part of their defense team right off the bat. Not all appeals are successful. Successful appeals can carry different things: from being sent back to the court and ordered to retry, to the defendant being given the opportunity to a plea bargain, to being remanded back to the lower court for a different sentencing...it just depends on the what grounds were used for the appeal.