About the Skill:
Sometimes the only thing that stands between an adventurer and fabulous wealth is a simple lock. When confronted with a locked chest, the Lockpicking skill is one you are sure to need.
Although a Mage may open some locked chests by way of the Unlock spell, only a well trained picker can hope to open the more valuable chests dropped by Paragon creatures and found during Treasure Hunts.
On the other hand, only a Mage can unlock a chest barred with the Magic Lock spell.
In order to attempt to open a target chest you must first acquire some Lockpicks. Use these on the target lock and you will attempt to break it. Depending on the complexity involved versuses your current skill you have a chance of breaking the pick altogether should you fail, so a well prepared rogue brings plenty of extras.
Note that often after disabling a lock, you may still have to deal with a few Chest Traps. The Remove Trap skill can be used to disarm these; however it's a risky business. It is often easier (and far less dangerous) to cast the low level spell Telekinesis on the target prior to opening it with your hands (from a safe distance, of course!).
How to train:
0 - 30: Train at NPC Thief or Tinker.
After 30 skill, you must either create your own boxes, or use a lockpicking house. You need one box of each type, that you pick and lock over and over again. If you stop gaining, you need to move on to the next box.
30 - 50: Pick locked boxes made by 50 skill Tinkerer.
50 - 70: Pick locked boxes made by 70 skill Tinkerer.
70 - 95: Pick locked boxes made by 100 skill Tinkerer.
After 95 skill there are 2 different ways to reach Grandmaster.
Method 1: Pick level 4 treasure chests in dungeons or do level 4 Treasure Maps.
Method 2: Go to Twisted Weald, attack a Satyr, and lure it over near the sparkling entrance/exit teleporter. Leave through this teleporter, re-enter, and then attack the Satyr. You must repeat these three steps until you are under the effect of its Discordance. When your skills drop jump into the sparkle teleporter and start picking boxes. When your skills return to normal repeat the process. You should reach Grandmaster in a few hours.
Addendum: After being discorded, leave via the sparkle and come immediately back in. The Satyr will no longer target you, but as long as you stay close to him you will stay discorded forever. Be careful, as sometimes the pixies will remain aggressive toward you. Just keep going in and out via the sparkle until you are both discorded and nothing is aggressive toward you.
For further explanation of this see Satyr Trick.
This trick can also used to create a 70 skill box with a Grandmaster Tinker.