Tips
Your skill cap level for lockpicking is your character’s level multiplied by five. If you are level 30, this means you can reach 150 skill level in lockpicking.
* Pick Pocket while leveling. This will give you junkboxes, which you can open to gain easy skill points.
* Get 
Dark Leather Gloves. It will increase your lockpicking skill by 5.
* Always carry 
Thieves’ Tools to open lockboxes.
For Alliance 1-110 – Redridge mountains
You can find Practice Lockboxes inside the mill here. Once your skill is 70, go to into Lake Everstill and open Waterlogged Footlocker. Practice until you are at 110 skill.
For the Horde 1-110 – The Barrens/ Ahsenvale
Enter the ship by the frontside. Head downstairs to find the room with Buccaneer’s Strongboxes in it. After you reach 70 skill, lead to the Zoram Strand in Ashenvale and look for Waterlogged Footlockers. Lock up until you are 110.
70-110 for both sides
Alternatively after 70 you can go to the Stonetalon Mountains and look for the Battered Footlocker within Windshear Crag.
110-150
If you chose to practice your lockpicking in the Stonetalon Mountains in Windshear Crag, you’ll have the shortest way to your next step of training. Just to the southeast of the Crag there is Windshear Mine. The Battered Footlockers here are actually of a higher skill level than the ones outside in the crag.
You can also up your skill at Hillsbrad Foothills.
In both the upper and lower levels of Durnholde Keep you can find the higher level Battered Footlocker as well.
There are many Battered Footlockers along the shore in Wetlands, which will require a lockpicking of 110. Here you have to focus on the ones INSIDE the camps and not on the outskirts. At this point, you should be somewhere around 150/
150-200
Waterlogged Footlockers in Desolace help you to skill up to 200. At this point, you should have water breath potion or Warlock’s buff.
Alternatively, you can level up your skill from 175 to 200 by Mossy Footlockers in Swamp of Sorrows.
From 150-175 lockpicking, in Badlands Angor Fortress head upstairs and open the Battered Footlockers. Once you hit 175, go back down and open Dented Footlockers to reach 200 lockpicking. These lockboxes sometimes don’t give skillpoints for picking them, but they are so close together, most players tend to come here at this stage, just for the convenience.
200-250
Run all around inside The Slag Pits in Searing Gorge to find Dented Footlockers. While you’re looking for them, pickpocket any humanoids so you can collect Sturdy Junkbox too.
After getting to 225 in Lockpicking, you can go to Azshara where there are Mossy Footlockers all along the shore areas that will take you the rest of the way to 250.
Or you can go east of the Caverns of Time in Tanaris and pick the Dented Footlockers.
250-280
Look for Scarlet Footlockers in Tyr’s Hand in Eastern Plaguelands. Make sure to pickpocket humanoids while you move between box locations.
280-300 – Blackrock Depths
Once you enter Blackrock Depths go to the left. Pick the lock on the door you see there. Turn right, open the door you see there too. Now head left and unlock the first door you find. Leave the dungeon the way you came and reset it. Repeat several times.
Another way is to stand on the bridge at the center of Ironforge/Stormwind and open lockboxes for people.
