The best things to pickpocket are things one or two levels lower than you, especially if they are in clusters(makes Distract more effective).
Make sure you use Distract as often as possible, especially if their backs are against a wall and you won't be able to sneak behind them without being seen.
The thing to remember though is to always pickpocket from behind, unless you are pickpocketing from a mob much lower level than you. You normally won't be seen if you are stealthed and behind your opponent, which often makes things difficult on moving targets.
If you are getting seen too often or your pickpockets are resisted, try going for lower-levels. If you think it will help, put some points into MoD (That doesn't mean you can pickpocket things higher level than you though, they will still resist as often as before).