1. Pull off all your mail [or at least anything you care about]. One expansion they lost all the mail. We got most of it back but were without it for a week or so before it was restored.
2. Make sure your quest log is in order. Some people are stocking up dailies and some are just clearing the log of clutter.
3. Check your bank and void storage – make sure you have space.
4. Be prepared just in case there are server restarts/downtime.