File names should be concise for a variety of reasons:
In DOS, files were constrained to a maximum for the name of 8 characters plus an extension of up to 3 characters. Windows now allows much longer file names, but the considerations listed above still apply.
For many of the same reasons, URLs should also be concise. Relative URLs are shorter than full URLs, especially if they refer to files in the same directory as the linking page. This might be a reason to avoid using subdirectories where possible, or to make directory contents fairly encapsulated, with few links between files in different directories.
Some kinds of redundancy may be allowed as a safety measure or to provide for greater flexibility in reorganizing the files. For example, it may be useful to give the same short prefix to all the HTML pages in a given directory to avoid conflicts if directory contents need to be merged at a later date and to make the identity of individual files clear when they are transmitted out of context.
Unless you are allowed to change default server settings, your home page will probably have to have one of a very few predetermined names, typically index.htm, index.html, or httoc.htm. Conversely, such a file name will not be available for other purposes (so, you may not be able to call your site index index.htm).
Many non-alphanumeric characters should not be used in file names. Sometimes what is allowed varies from server to server or from time to time on the same server. For example, even though the ampersand (&) is a legal file name character according to the relevant HTML standard, the FIMS intranet started a while ago refusing to deliver the file dispa&a1.gif and reporting falsely that it could not be found, even though it in fact existed at the address specified. As a result, the file had to be renamed dispa_a1.gif, and the link to it had to be changed.
Some servers treat upper and lower case letters as the same and some treat them differently. So, you should not use case variation in naming your files. Instead, you are advised to use all lower case.
Of course, extensions should always match the file type. Putting the wrong extension on a file name leads to inappropriate and inconsistent behavior on the part of browsers.
Sometimes, a brief naming scheme will suggest itself fairly readily. For example, if your site includes a newsletter that is published monthly, you might call the files news followed by 2 digits for the year and 2 digits for the month (news0312.htm, etc.).
Once exceptions start to arise, you will need a standard way of dealing with them. For example, suppose one month you decide to issue two newsletters. If it is important to have all the newsletter files sort in date order, you might decide on a general rule to add the day of the month to the name of a second or third newsletter appearing in any given month (news031215.htm, etc.).
Naming a file should not require too much effort. Having content divided among files according to subjects that can be represented by brief, distinctive key words or phrases can be a great help in quick file naming.
If you must rename a file, you should provide for redirection: if you have access to server options, you may be able to get the server to redirect users of expired URLs to the correct pages automatically; otherwise, a good idea is to leave stub pages with the old names that redirect to relevant renamed pages. It is good etiquette to advise visitors explicitly when a redirect happens, so that they know to update their bookmarks.