Peek is the skill in First Dawn which is absolutely essential for an aspiring Thief. It allows the player look into the inventory (meaning player and NPC backpacks) of others. This means that the skill must be learned if the skill Stealing is supposed to be of any use, as without it, the thief can only steal random items, instead of something specific. Snooping only works when standing directly beside the character and can be discovered, thus the skills Hiding and Stealth are most useful.
There are not many tips training this skill, as most is just using it. However, one good tactic is to target Shopkeepers, as with no player near by, they are easy targets for peek.