There are locked doors throughout World of Warcraft, as well as locked chests in the environment and locked boxes that can be looted from enemy bodies. Blacksmiths can craft keys that will unlock some chests, boxes or doors. Engineers can also craft "charges" to blow open some doors or chests. However, these items require specific materials be used to make them, so many blacksmiths and engineers don't keep them in stock.
Rogues can readily
open any door, chest or box if their Lockpicking skill is near the maximum level of 375 (350+ should actually be enough).
This is just a nice quick overview to increase your lockpicking skill. For an in-depth guide that also includes gold making as well, take a look at this WoW profession guide.
In fact, some groups of players will prefer to take a rogue with them into a dungeon like Shattered Halls, just to avoid
taking the long way through a cave full of ooze creatures. But how do you get your skill up to the max
First, you can learn the Pick Lock skill from your Rogue Trainer at level 16 and you will need Thieves Tools to use it, you can usually buy these from a Shady Dealer or Poison Vendor. This item won't disappear when you use your Pick Lock skill, so you only need
one and you can use it repeatedly.
As a general rule, once you learn the Pickpocket skill, you can use it on any humanoid enemies (mobs) that you quest around. You can get extra money (copper/silver) this way and often you'll get boxes that you can pick if your Lockpicking is high enough.
You can't increase your Lockpicking skill without increasing your characters level. Each time you gain a level on your character you earn the ability to increase your Lockpicking skill 5 more points.
Up To 100
Engineers can craft Practice Locks that you can use to skill-up until your Lockpicking is 80, but you can only use each Practice Lock once.
Both Alliance and Horde rogues can get a class-specific quest at level 16. Alliance rogues must go to Alther's Mill in Redridge Mountains. The same quest for Horde will take rogues to a boat by Merchant Coast in Barrens.
Bloodelves can take a quest in Ghostlands to go to Amani Catacombs.
Each of these quests include locked chests that you can open for skill points, they will disappear when you open them and reappear (respawn) a few moments later. You will be able to get your Lockpicking up to the maximum for your level, which is your level multiplied by 5. If you are level 20, you can reach 100 Lockpicking this way.
Up To 150
At level 20, rogues of both factions can pick up another class-specific quest. The reward for this one is the ability to use poisons and the quest item you need is inside a locked chest, but you can pick this chest for skill-ups until atleast 150, probably more like 170 or even 175 if you keep at it. Opening the chest will give you a long-lasting poison called Touch of Zanzil, but you can use Anti-Venom from First Aid, or the racial Stoneform skill if you are a dwarf. When you turn in the quest you will also receive an item to get rid of this debuff.
You'll need to use your Pick Lock button before you'll be able to click on this chest.
Up To 200
You can visit Badlands and go to Angor Fortress. The requirements to open boxes here range from about 150 to 175,
and by 175 you should definitely be able to open all of the locked boxes.
Or you can find locked boxes underwater along the coast of Desolace, but you might want to bring along an elixir of waterbreathing so you don't have to die in the process.
You should be able to get above 200 Lockpicking using one or both of these methods, in addition to pickpocketing humanoid mobs of the appropriate level.
Up To 250
Once
you are about 205 Lockpicking, you should be able to go to Scarlet Monastery in Tirisfal Glades. There are 4 dungeons there for characters between levels 33 and 40, two of them (The Armory and The Cathedral) are locked. You can pick the locks and go inside, Pickpocket a few of the mobs and go back out, the timer will reset so you can pick the doors again to increase your Lockpicking ski
