Here is my 5 things to keep in mind:
- This is a BETA. Things are changing constantly, quest lines are changing, what you do now, may be completely different next update. If you want to provide valuable input, check the Blizz forums. The way a quest works, or what you need to do something is flexible at this time. Contribute.
- Expect regular downloads. Beta is not on the regular maintenance window. Major enough bug, you may have to download all 25gb again. I just downloaded a 3GB patch since last week. They appear to have a planned reboot each Monday, but as problems arise, they will reboot mid-day, and they do.
- Bugs are being fixed. Expect problems with quests, skills, mini/quest bosses and even dungeons. The pink blocks in this bug were part of the view. Lowering my view resolution from HIGH to GOOD fixed this issue.
- Addons may NOT work. In fact, Blizzard disabled all addons during Cata beta until about 2 months before release. Get used to the standard interface.
- Don't feel attached to anything you do. You don't keep your character, gear, etc. Starting off, you can 1) create a new toon and start at one leveling up, 2) copy your existing toon over or 3) copy over a pre-made character over in top level tier 13 gear. For options 2 & 3, log on to battle.net then access your beta license and copy (see forum post).. Pre-mades come level 85, fully equipped and with 4000g. No point starting the new Panda raids using my partial Tier 13 set, when I could start off with 4-piece set bonus.
Otherwise, have fun!