Also, take advantage of the tools you have in the Import module. Add your copyright to the EXIF data, and apply any tags that are universal to the import. Saves from having to do it later.
Oh, and I forgot, for tagging old photos there's this Spray Can tool at the bottom of the Library module where you can enter a set of keywords and then just click on the appropriate images in your current folder view. Makes life really easy if you have a bunch of shots from a day where a certain tag(s) applies randomly throughout. Just put the keywords in and one click adds them all to that shot. I forget about this all the time and get angry when I remember it after doing it through the right panel for 2 hours.
Wow, now thats cool. I have never even explored the paint can. Thanks for that tip.