Be alert in large crowds, or anywhere people are pushed up against each other such as subways and other forms of public transportation. Be cautious of anyone who bumps into you, as incidental as it seems. Pickpockets can work in teams in less crowded areas as well to make incidental contact seem more natural.
Watch out for drunks, especially an attractive one. She'll stumble around pretending to bump into people or touch a man affectionately and pick his wallet while he's distracted.
Keep an eye out around ATMs for suspicious observers. Some pickpockets stake out cash machines watching where people put their money--it also lets him know who is carrying cash around.
Spot anyone who is constantly looking over her shoulder. Pickpockets often do this to make sure no one is watching.
Decline help from strangers who offer to clean spills off of you. There is a lot of patting and rubbing allowing pickpockets opportunities to swipe things. He may have even caused the spill on purpose as this is a common trick.
Notice people who are wearing nice clothes, a suit or dress perhaps, but with sneakers to make a fast getaway. They may also be carrying a jacket or newspaper in one arm to disguise what the other arm is doing.
