Has the appimage people formulated best practices on how appimages should look like?

Are there a list of best practices about how a appimage of a program should
appear? If so where is the list to be read? I have a suggestion about
a best practice regarding how updating a given appimage program should
get done. Thanks.

I think everything you need should be here: Packaging Guide — AppImage documentation

Updates are described here: Making AppImages updateable — AppImage documentation