When most people play World of warcraft, they want what we want in life. Money, power, women/men, all the good stuff. Now if you haven started playing cataclysm yet, there are definitely some things you need to know. Once you load that disc and start the cataclysm, you need to have all of your items in order and all of your plans thought out. Once you go in, there is no going back.
The first thing you need to do is finish exploring the map. Once the cataclysm hits, there will be no way for you to get the "Explorer" title. If you one of those players who love achievements, then you will be sorely disappointed if you don grab this one now. While you are grabbing that achievement, you should be going after all the other achievements you either didn have time for or couldn finish. You may never have another chance to finish them off.
The second point may seem obvious, stockpile gold. Now, you may be thinking that should go without saying, but it is the most important thing you can do. With a new world comes new item. New items that will be very expensive. Now would you rather blow your whole nest egg on a sweet helmet or a new set of armor complete with sword? You do the math on that one.
While you grabbing every last piece of gold you find, you should be leveling you profession to max. This will help you once the cataclysm hits. Everyone need services with all the new items. You can corner the market and get back all the gold you blew on that shiny new equipment.
All that new equipment will also get you some attention from guilds. If you one of those social players, you should earn in as many factions as you can. A huge part of cataclysm will be Guild Leveling and exalted reputations will make you look like the prize hen of all those players wandering around with their head cut off.
Finally, you should grab yourself a guide for cataclysm. No matter how good of a player you are, someone out there has found something that you don know. Some nice tips are out there but if you want the real meat, you should really pick up a full guide. It makes a difference no matter how you play the game.