Many photographers like to rename their original image files. I personally don’t — I look to the folder name and image keywords I have applied to tell me about a photo rather than the file name, so the camera-generated file name is fine for me. There is no right or wrong on this — I suggest that you come up with a system that makes sense for you, and most importantly, stick with it for consistency.
Even if you don’t rename your originals, you may still find that you want to rename copies that you export for email, Shutterfly, Zenfolio, etc…
I have produced a short video to show you the basics of how to set up and apply a filename template that you can use to rename your files, whether during import, after import in the library module, or during export.
Click HERE to watch the video. [UPDATE: This is an old video with not-great audio and it requires Flash to watch it, but it is applicable to later versions of Lightroom. The only difference is where Renaming is in the Import dialog – in Lightroom 4+ look for it in the File Handling tab on the right side.] Note that in the video when I show the template editor drop-down list, Edit is cut off — but it is the last choice.
One note on export: if you have arranged your images in the Library module in any other order other than filename and you want to preserve that order upon export (for example you want them to show up on Shutterfly in that order), make sequence number your first field in your renaming template.