One of the most obvious changes is also one of the most commonly forgotten: system requirements. While World of Warcraft still has relatively low requirements, they have gone up, so anyone that has difficulty running the game now will need to keep that in mind. Besides, the new areas are quite beautiful and truly add to the game experience.
Turning off add-ons can help with issues running the game by freeing up memory, and many will likely become obsolete or broken upon upgrading. Luckily for add-on junkies, the major mod designers have had access to beta for some time and should have updated and compatible versions around Mist of Pandaria’s launch. The streamlining of abilities should make spell management add-ons less necessary, but the new resource systems for some classes may become easier to manipulate with the proper add-ons.
Account-wide achievements, mounts, and pets mean that you no longer need to earn farm on each character. Most of the more difficult and time-consuming achievements have become account-wide, like What a Long, Strange Trip It’s Been. You only need to get the raven lord and hyacinth macaw once, and all your characters forever will have them to use. Save your gold and time.
Speaking of gold, new expansions give players a chance to really rake in the gold, if they know how the market works. Gathering professions can make a pretty copper by snapping up the new Pandaria leathers, herbs, enchanting mats, and metals and sticking them on the Auction House for exorbitant prices. Scribes that get lucky on monk glyphs can make hundreds—if not thousands—of gold per glyph, so a savvy scribe might stockpile low level inks for the low level monk glyphs. All of the fresh characters will push up the prices and demand on lower level crafting materials because many would rather spend gold buying materials than spend hours gathering them.
Check out the changes to your class. The talent revamp alone will take some getting used to, but the spell and mechanics changes will hit the hardest. Hunters lose their melee weapons and thus melee abilities like Wing Clip in exchange for finally losing the minimum range requirement for their ranged attacks. Warlocks—especially non-affliction spec—are getting an entirely new resource system, so keeping abreast of the changes might make acclimating to them less of shock.Decide whether you want to make a new character and whether or not you wish to make it a monk. New expansions are excellent opportunities to reroll, and the simplified and streamlined leveling and ability selection makes learning a new class easier than ever before. Besides, a great deal of players roll new characters for expansions, so joining that wave of fresh levelers will guarantee faster queue times for dungeons and battlegrounds, help for questing, and plenty of enemies to engage in world PvP. Should you set your heart on a pandaren, keep in mind how crowded their starting zone will be for the first couple of days. As long as you can deal with the cutthroat competition for gear, rolling a monk should be fine. Check out the various fight animations unique to each monk race before choosing one to make sure you pick your favorite. You will see them constantly. If you have name picked out for your new monk, make a random level one character with that name to hold onto it so nobody else can snap it up.
As for Pandaria itself, it will be crazy overcrowded for the first couple days, so you may have some lag issues depending on your internet and computer quality. Otherwise, the crowding has some positive effects, such as leading to the faster queue times, questing help, and world PvP mentioned earlier. The vast numbers of players from both factions tends to keep ganking to a minimum during the early days of each expansion, and Cataclysm made it so you no longer have to struggle to tag quest enemies the second they spawn.
The single most all-encompassing and important piece of advice I can give is simple: take your time. Enjoy leveling and running lowbie dungeons. Take it from someone that has done serious endgame raiding, arena, and the vanilla PvP grind: rushing just burns you out. It also tends to create a vicious cycle of burning out, taking a break, rushing to get caught up, burning out again, etc…. Even Blizzard wants players to take it easy and play more casually. Enjoy the journey and the destination.