Keep The Heat Constant

This one is almost always wrong. With the exception of some kinds of heat pumps, it is always a good idea to adjust the heating or cooling temperatures to the current needs. Setback thermostats are one of the few energy saving devices which will likely pay for themselves in one year.

By the way, houses need some heat, so it's best to set the lower temperature setting to between 50 and 55 degrees.

...and for some tips to reduce your cooling needs, see: Air Conditioning