Picking up herbalism and mining is the best professions to have while leveling. Not only will you earn gold as you level, but you will also get extra XP. At level 20 you will get over 500 XP for picking up a ore or a herb while killing a mob only gives a little over 100 XP. Don’t go out of your way to pick herbs if you are trying to level quickly, but pick the ones that are on your way. Leveling from 110 to 120 can be done pretty quickly just by doing this. There are a few items that will help you if you decide to use professions while leveling:
You can earn a decent amount of XP by doing Herbalism or mining. Any zone works but I prefer Sholazar Basin as a lot of the mobs are not aggressive and the mobs are spread out so you will find a lot of herbs and ore that you don’t have to fight for. It is possible to make about a level every hour by doing this, or a level every 30-40 minutes with rest XP.
This is a once size fits all pet farm that can generally leave you with a small sum of gold if your server is low on this specific pet. (You can always check on the undermine journal). It takes place in the Ihgaluk crag and is generally performed by sweeping the oozes in the small muddy pools surrounding the area. An easy spot to hit, that really isn't farmed all to often. I was able to get one in the video after a small 24 minutes.
This spot actually kicks BOOTAY. And I only say that because it's so hidden, unique and quirky that I had to add it to this list, despite it being a method rather than a farm. Generally what you want to do is some sneaky arbitrage. We'll be buying the items Royal olive, Dalapeno Pepper, River onion, and Muskenbutter from the vendor for 2g – and reselling them to the AH for 4g+. This is an awesome way to take advantage of players laziness and the demanding reagent requirements for some of the higher end recipes. By selling from the vendor to AH, you can make easy gold – in fact I suspect most cooks do not know these reagents can be purchased from NPC's.
Heirlooms: Heirlooms are the best source of bonus XP for leveling. All slots can be gotten pretty easily now, except the rings. The time you need to spend to get the rings if you haven’t gotten a level 3 shipyard in WoW is way too long, so getting the rings is generally not worth it. Having all your heirloom gear will boost XP by 55%. Generally, you want heirloom gear with crit on for leveling as you want to kill mobs in a few hits as possible
You have a new best friend, and his name is M, the key you press to bring up your map. Your active quests will be highlighted on the map; if you click one of the highlights, this quest will be tracked on your minimap. This means you’ll get a compass heading pointing you to the nearest quest objective, AND quest-relevant regions will be highlighted. How convenient!
This new farm takes advantage of the level scaling changes implemented by blizzard. Event NPC's like the NPC's found in the twilight outpost, scale up or down depending on your level. HOWEVER, your level also determines which loot tables each mob will have. By using a level 58 character, you can successfully loot items in the 57 – 59 item range, a range which has some of the most expensive and well sought after transmog items in the game. In less than 30 minutes farming this spot I was able to snatch up some glorious legplates[/URL] (on video) – worth a stunning 150,000g. Watch the video for absolute details I suppose, but the gist of it is you need to create a level 58 DK, go to the twilight camps, and start the killin'. Unlike before, an implementation of a daily event has changed the loot tables! This spot is the new hot thing on the block.