Except for bellhops and service personnel in International Hotels, tipping in Taiwan is generally not expected.
For restaurants (especially in large hotels), if there is a tip to be taken, they will just add 10-15% to your check. Even very small family style Taiwanese restaurants are doing this now (usually no more than 10%), so if you are sensitive to service charges -- ask first. But in general don't worry about tipping when you are eating out! If you are from the USA, this may take some getting used to...
It is not necessary to tip Cabbies -- in fact it will confuse them. But if the balance is not too much (say, 5 NT$) and you leave it (i.e. tell them to keep the change - "bu yong dzao" ) It is appreciated.
There are other exceptions to the no-tipping culture, too - for example, if you are adventurous and go to a spa or "beauty parlor". You should slip the service person 10% or maybe 100 NT$ (about $3USD) for good service. However, if you are at this level, you probably know a native that you can ask for advice...
Never stand your chopsticks up in your rice bowl - it is seen as food left for the dead, which is usually done at funerals.
When beckoning someone over, e.g., a waiter, your hand should be palm down to be polite, not palm up as in the western world. Tapping your thumbs on the table is a compliment when eating (Just don't do drum rolls). A gracious host will tell you the food isn't as good as he wanted it to be. If you tell him that it is much better than you've had before, he will appreciate the comment, but may still tell you it could be better. That is common and because of them wanting to be humble
Thank you in Chinese sounds like zjay zjay (Xie xie)