Appeal deadline questions after an unemployment denial - any advice?

I got a denial letter last week saying I left my job voluntarily, but I was let go as a customer-service rep. 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.