Mainly in crowded tourist areas such as clubs, malls and buses/traffic lines.
Keep an eye on your belongings and know where your purse is at all times.
If you're a man, keep your wallet in your front pocket and avoid pulling out large amounts of cash in public.
Best to separate smaller amounts into a separate pocket or money belt so as to not attract anyones attention to a large wad being flashed for everyone to see.
If you're a woman, keep purse in front of you or, better yet, carry a back pack and carry it on your chest as you travel into a crowd avoiding easy target for "cutters" which will run up, slice your bag and get away with your valuables before you know it.
Avoid being distracted by small groups of people and simply smile and walk away if you feel uncomfortable.