Make the purpose visible
For new working files, choose a name that describes the contents. Include a project name or a date when that helps you distinguish similar documents. Avoid changing system or application files as part of a tidy-up.
Choose a modest convention
Pick a simple pattern for your own documents and use it consistently. Keep the convention short enough to remember. A familiar name is more useful than a clever code you will need to decode later.
Test before expanding
Try the pattern on a small set of new documents first. See whether you can find them again without opening each one. Leave shared and linked files alone until you understand how changing them affects other people or tools.