I thought I would make this guide since I get asked as a rogue all the time what the easiest way to level up your lockpicking is. I have tips for both horde and alliance to get your lockpicking from 1-300 pretty easy. Having it at 300 is the best thing because you don't need to worry about keys for doors, there are exceptions though. Since the keyring was added keys don't take up space, but you could still pick a lock before you get the key, like the searing gorge key.

In addition to the steps below, make sure you pickpocket any humanoids that you can, hopefully they'll drop chests. If you can't open it up then save it for when you are at that skill so you have a fast boost. There is also footlockers in various locations that you can use for skill ups.

You can also sit in town and open boxes for people. You don't get much business this way but it does help you level for free.  Before I start, you need to realize this is not a leveling guide, it's just a guide that will help you become a better lockpicker, if you need a leveling guide, the best ones are: Joana's 1-70 Horde leveling Guide for horde, and Brian's 1-70 Alliance leveling guide for alliance.

Step 1 : (About 1-75) Do the Initial Rogue lockpicking quest

Horde:
This entails feeding a parrot a cracker close to ratchet, then unlocking the chests on the boat. You want to do this until the chests are grey to you, and ya, its going to take a while.

Alliance:
You're going to go to the tower in Lakeshire and open them up until they're grey to you as well.

Step 2 : (About 75-175) Poison Quest

Horde:
Little known trick, while doing this quest in the NW barrens in the Venture Co. area is a chest at the top of a tower... Repeat what you did in Step 1. Open that chest until it goes grey... That'll help get you passed or up to 175

Alliance:
Similar to Horde. While in the tower at Westfall keep opening the chest at the top until you reach about 175. May be hard if the boss aggro's you so bring a friend or level up. The chest will curse you every time you open it so if you do this after the initial quest you have to get a cleanse.

Step 3 : (About 175-250) Scarlet Monestary (see step 4 if to hard)

Horde and Alliance:
You can first start with unlocking the door into the instances but this can only be done about every 10 minutes per door. If you don't wait then it doesn't count as skill up. So just pick them then run into the Cathedral. Jump into the left locked door and into the cathedral instance. Sneak up, or run if you can avoid being aggro'd, and pick the cathedral door then run out and reset. If you find you are too low to start on the door because you are too lazy, jump into the first instance and pickpocket everything in there. This is of course, making sure you have your stealth maxed to avoid detection. You can repeat that as many times as needed, but if you followed step 1 and 2, the cathedral door will get you to 250. This step can take longer than when I originally did it since you can only reset an instance 5 times an hour.

Step 4 : (About 250-280) Pickpocketed Boxes or Various Footlockers

Horde and Alliance:
Like mentioned at the top, when you pickpocket mobs and they drop boxes you can't open yet, save them and when you can open them you'll get a big fast boost. Once I opened up the SM doors to 250 I had heavy lockboxes I used and got 20 free points. Pickpocket and lockpick them until your heart is content. Although SM is more effective cause of the respawn, it is better then getting pummled by elite's. You also want to go around to zones that are within your level range and find footlockers.

Step 5 : (About 280-300) Black Rock Depths

Horde and Alliance:
All you have to do now is lockpick inside BRD until 300. What you do is go into BRD and turn left and open up the 3 doors. Rinse and Repeat until 300. You get a max of 3 skill ups per run.

There you go and congrats 300 Lockpicking!