There are a lot of methods out there for Pickpocketing so I will include one I found useful below. In order to Pickpocket, you need to sneak up behind someone and select them with X. Your pickpocketing chance of success depends on how many characters are aware of you (the red "eye" indicator over NPC's heads when you are in stealth mode) and your stealth skill.
Personally I found that simply working on this a little bit at a time (especially with enemies that I was planning on backstabbing for the
Working on it as such, I unlocked the trophy shortly after arriving in the town of Didenhill, a few areas into Dalentarth. For an ultra fast method (courtesy of YouTuber ObsidianDraconis), see the video attached.