Titles of media files should be meaningful and helpful in the language chosen.
Avoid "funny" symbols (control characters, unneeded punctuation, etc.) that might be significant in future wiki markup. It is a good idea to stick to graphemic characters, numbers, underscore (space), ASCII hyphen/minus/dash, plus, and period (dot).
Except for minor technical corrections, files should be uploaded under new names. The file name applies to one concrete work: do not overwrite it even with a similar image of the same subject. See Commons:Overwriting existing files.
File names may be up to 240 bytes long, a filename over 240 bytes may break horribly when uploading a new version (As the date is prefixed to the filename for old versions of the file which takes 15 bytes). English filenames will usually use 1 byte per character (some symbols may fall outside the ASCII character set), but for other languages, or cases with non-ASCII characters, 240 bytes may be much less than 240 characters, as these can take up to 4 bytes per character.
Tip: Keeping the filename reasonably short reduces need for truncation when the file is downloaded, e.g. on CD:s filenames are limited to 31, 64, 197 or 207 bytes or characters, depending on extensions used.
Tip: Use the 20 first characters for essential information, as those will show up on category pages.
Files can be renamed after they have been created, but only under some circumstances, as this breaks inbound links. It is therefore important that a good name is chosen when the file is uploaded. See Commons:File renaming.