Denied unemployment, how do I appeal? - 25 weeks in

My claim was denied after 25 weeks of waiting, and the letter says I have a short window to appeal. I have read a lot of threads here and could not find my exact situation. The letter lists a deadline and a hearing process, but it is hard to follow. If you have appealed before, what helped you prepare?

File the appeal before the deadline, even if you are unsure. You can gather documents afterwards. That is the one part I would not wait on.