Keep an eye on your stuff, particularly when walking around.  When you get in at the airport, go upstairs to the departure area to get taxis that just dropped off passengers; the taxis who wait for new arrivals overcharge. 

New traditional Filipino cuisine restaurant in Quezon City, near the Sulu Hotel.  It's called Adarna, and they have very good food.  Highly recommended.

Best bargain shopping, if you're up for a little adventure and heat, is in Divisoria.  Take the MRT north to Quezon Avenue, then hop on a jeepney to Divisoria.  It's a district of stalls and bargain shopping. 

Bring lots of water.  Be polite, but careful.  Although there are a lot of nice people in Manila (and the Philippines in general), there are always a few jerks who try to take advantage of travelers, especially if you obviously don't look Filipino.