If you're a foreigner, avoid being alone in shopping areas like Greenhills, and malls like Megamall or Glorietta. For sure, robbers will eye you and steal your wallet. And they're good - you'll only notice it when you need your wallet for something.
Avoid going through rush hour traffic, especially during friday, and most especially during the Christmas season. You'll be stuck on the road for a minimum of two hours.
Avoid riding the MRT or LRT during rush hour, they're usually jampacked!
When crossing the street, avoid cars, motorcycles, buses and jeepneys. In the Philippines, not a lot of people give importance to the pedestrian lanes. I'm from here and I hate crossing streets here.
On a lighter note, if you go to a shopping place with stalls (not the malls) like Greenhills, avoid buying an item with the first price that's given to you. HAGGLE! It's fun!
It's still fun here, because thieves aside, the people are friendly, funny, and pleasant. :)