Tipping [Hongbao] Practice
Red packets [“Hóngbāo (红包)” in Mandarin] are commonly presented at social and family gatherings during the Lunar New Year. The red color of the packet symbolizes good luck, happy and energy; and giving out "Hongbao" is symbolic act to send good wishes.
Red packet always contains money, varying from a few dollars to several hundred (the amount depends on how close the relationship is -- or if you are trying to show your appreciation for "a job well done", in the case of an employee or member of staff in your residence or office). The amount of money in the red packet should be in even number -- odd numbers are associated with the cash given at funerals (帛金: Báijīn - money placed in a white envelope in contrast). Amounts in 6 ("Liù" in Mandarin, same pronunciation with "smooth") and 8 are good choices (they are the lucky numbers in Chinese culture).
Traditionally, those who were married or elderly would give out "Hongbao" to their younger unmarried acquaintances -- although nowadays it is often common for grown-up "children" to give "Hongbao" to their parents and grandparents as a sign of appreciation. In Hong Kong and Guangzhou, it is also a custom for employer giving employee "Hongbao" on the first work day after Chinese New Year holidays, and in some companies, married employees usually pass out "Hongbao" to their unmarried colleagues as well.
Although tipping is not common in China, Lunar New Year offers a good opportunity for you to praise your ayi/driver's good services. You can give him/her a red packet as a recognition/encouragement as well as good wishes. Regarding how much should be in the red packet, it is really base on your own judgment. Some employers will treat it as a bonus for the great services and give a "Hongbao" commensurate with 1-month's salary (pro-rata basis is suggested if they have been working for you less than a year), but the amount is really up to you and how you want to show your appreciation. For members of staff in your residence, a red packet containing RMB20-100/HKD20-100 or a small gift is considered an adequate gesture.