To successfully steal an item without getting caught you must take it in crouch mode with the "hidden" description viewable on your screen. However, there are items that are constantly guarded or require a very high Sneak skill. To steal those items easier, you can use the "Grab" ability. Simply grab the item and move to a darker part of the room until the "detected" description turns to "hidden".
When you see an item on a shelf or table in a store or house where there are too many people around to steal it, walk over to the item, get it in your crosshairs, and click the Right Analog-stick to pick the item up. Then, take the item to an area where no one is, drop it, and steal it. For example, use the Bottle Cap Mine in the Craterside Supply on the work bench, pick it up, then drop it at the end of the desk to the right, next to the two metal boxes. Enter Sneak mode, get next to the desk once your indicator says hidden, and steal it.
