While Sun Moon Lake (riyuetan) is a popular tourist destination, I cannot really see the attraction of this place.
There is nothing much to see there, save for an impressive looking Chinese temple, and that's only if you like viewing temples. The cruise across the lake is really nothing to shout about, and there's nothing much going on in the small settlements around the lake. And people there sleep very early, so there's nothing to do at night.
Unique Suggestions: Don't stay too long.
Sometimes, when you hire the services of a cabby to take you around for one day, the cabby will take you to a tourist shop where you will be subject to high pressure sales tactic in order to get you to buy some ridiculously priced and useless object like jade carvings or high grade green tea or honeycomb moisturiser.
The sales people will follow you around the shop and constantly bombard you with their sales pitch which can include, but is not limited to, flattery, and a constant reminder that they accept credit cards.
Unique Suggestions: If you don't want to buy anything, firmly walk out of the shop because I can imagine, if you're weak willed, it's not easy to escape their clutches.