Tipping is done and perceived differently all around the world. I don't really have much money at all, but I still feel it's necessary to tip well according to common local practices. What are the common pitfalls or mistakes that are made when tipping in the Philippines?
Tipping can be a little weird here, in general restaurants will add 10% service charge and not expect much else (if they don't add it feel free to leave 10%). Over and above this people often leave some of the change from the bill to round up to the nearest 100 pesos or something.
Bars don't generally expect a tip (i.e. it's not like the US) but feel free to buy a drink or leave the equivalent amount if you think they've been helpful.
Anyone that helps you out (porters, guards, doormen, etc) will appreciate, and perhaps expect, a small tip. Maybe 20 to 50 pesos, more if they really went out their way to help you. But note plenty people will try and help you even if you don't want it -- i.e. flagging down a taxi that you could easily have done yourself, opening the door, etc, don't feel compelled to tip them. Some places have signs saying not to tip people acting as guides or helpers as they're already salaried, again it's up to you.
You'll never get a bad reaction from over-tipping or tipping where it's not expected. Similarly nobody will chase you down the street for not tipping. Your mistake will probably be tipping too much.
Many people are earning between 100 and 300 pesos a day in service type jobs, so even a small amount of money is fairly significant. In general if someone provided a service you felt was useful feel free to reward them for it. There's no reason not to tip what you personally think it's worth, just be aware your probably paying too much.
If your staying in one place or frequenting the same places it's an idea to tip some just to encourage better service. However if you get a reputation as someone that goes around handing out 100 pesos notes for any little thing you may get more attentive service than you can handle.