A criminal appeal must be handled appropriately because there are many factors that you must consider. One thing to remember is that you aren't presenting a new case in an appeal. Instead, you are asking the appeals court to review what was already presented.
All appeals of criminal cases must be based on a legal mistake that directly impacted the outcome of or sentence in the case. These must be very clear. It can sometimes be hard to show that something happened that warrants the appeal being granted.
It can take time to get the case before the appeals court. You should remember that these cases do have time limits, so you can't waste time when you decide to file. The date that matters is the date that you file the case, even though it might take months before the case is reviewed.
Criminal appeals are handled through briefs. The court won't consider new evidence and will only look at what was already covered in court. There are times when you might be asked to address the appeals court. These are very short appearances that must be handled very carefully.
There are many things that the appeals court can do. If they issue a ruling that you don't agree with, you will likely have the option of taking to a higher court. The final stop in the process is the United States Supreme Court. While that court does hear many appeals cases, they are very selective in which ones they take on. Ultimately, most appeals are handled in lower courts.