I don't have to do many appeals, but when I do, if the insurance company doesn't already have an appeal form available, I have one I made myself, that I keep in my documents, and pull up and fill in accordingly. I also always send in a copy of the treatment note for the date of service, and any medical policies/LCD/NCD's for the insurance that supports why the claim should be paid. Also, if it is a specific item/service that is being denied as non-covered, be sure to have proof that the patient's policy does indeed cover that item or service, and send that in.
The last two appeals I had to do were for UHC, where they denied claims for custom molded foot orthotics, stating it wasn't a covered service under the patient's policy. But I had previously printed out the pages of each patient's benefits that clearly said orthotics were a covered service. So when I did my appeals, I sent those pages in also, and UHC immediately paid the denied claims.