1) Subscribe to this list so you can keep track of the ebb and flow of
Debian. (Probably you already do this.)
2) The cycle begins with you running the stable version, but refer to
it by its code name in your sources.list -- potato, sarge, etch,
whatever. Upgrade from time to time to pick up bug fixes.
3) When you start noticing complaints on this list that stable has old
outdated software that is way behind some other distribution, that is
much more up to date, consider making a dist-upgrade to testing, but
use the code name, not the word testing in sources.list. Maybe delay
doing this until you see complaints about oldness that specifically
mention features that sound interesting for software that you use.
4) If there are sprinkled in among these oldness complaints, other
complaints about e.g. X-windows being broken in testing, of course
stick with stable.
5) When you can set aside time to fiddle with new software for a
while, make the transition (dist-upgrade) to testing (using the code
name). (Even if the dist-upgrade is absolutely smooth and uneventful,
you will want to spend some time playing with the new features. And
there is a possibility that you will mess up something and take a
while to recover.)
6) When the next release happens, nothing happens for you. You are
already dist-upgraded to the new release. You already have the right
words in you sources.list. You get to work on whatever you were planning
to work on that day.