As far as files, make sure you include a .ips file of the JUMP Base ROM with your level in it, the .mwl files for your level, the .map16 files, a readme with information, and any custom music files, custom graphics files, or custom sprite files you used in your level.
I guess I'll put an example post here.
I am submitting my level wrote:I made an icy/snowy level called Siberian Precipice. It has five drrgon coins, two exits, custom music and palettes, and is overall pretty simple. More in-depth information is in the readme.
Some screenshots
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