We live on a very low (compared to most ex-pats here) retirement fixed income. But it's still a lot more than the staff in my building make each month working.
We give the cleaning staff and security staff a Christmas envelope with a 500 baht note each. I wish I could give them more as they really do make my life in this building much easier, but I can't afford it. The security staff stay awake and are very helpful, often running to open elevator doors for us if our arms are full! The cleaning staff are always right there when you need them, and unobtrusive when you don't!
Although American, I don't believe in the American style of tipping everywhere I go. But I do eat in the same restaurants every week and so leave the staff a small tip. Most are married with young kids and need the money more than I need another cup of tea.