How should I use heat tape?
Heat tape/line is often used as a bandaid for improper installation of the pipes to begin with. There certainly are situations where it makes the most sense, but in general, if you're below the frost line and inside insulated areas, the pipe should be fine.  

Think of it this way: if your power goes out for enough time, the pipe will freeze anyways, and if it bursts, you still have a major problem.

If the pipe is not buried deep enough, then you can either put it deeper, or add rigid foam on top and sides to help insulate it.

In a basement or crawlspace, it's better to insulate that space and make it suitable for running pipes, than to mask the problem with heat-tape (and get another thing that can fail).

In my experience, the heat line products that go inside the pipe seem to work much better. These work best when you also insulate around the pipe itself.



Often people put timers or thermostats on basic heat line due to the energy they use: these are both problematic. Timers don't regulate according to temperature, and thermostats measure the temperature of where the thermostat (or sensor) is, not the actual water. This is not so important with 6' tape, but definitely is with 10 or 100' runs.

There are products that are self-regulating: you give them constant power, and all throughout the line, if it's cold enough, the line (in the spot that's cold) will turn on and heat up. These use a lot less power, and are much more reliable (no timer/thermostat to fail). 

As far as installation, it's fairly simple, but there are some important notes:


Install on a GFCI-protected circuit 
Make sure the electrical receptacle, plugs, extension cords, etc are not in a place where they can be submerged in water (I have seem them in well pits outside)
Not all heat line cannot be cut: For these, you have to order it in exact length
Becareful not to damage the line during installation, as for many lines if they're cut or the contacts are broken the whole thing is garbage. This means: don't nick it, don't bend too sharply, don't crush/pinch it, etc.