In a (sort of) response to some of the refactoring posts that Brandon Savage has been posting, Dagfinn Reiersol has suggested something that should have been done from the start - write unit tests before you refactor.

That said, I do have something important to add. The series is missing the first, most basic rule: Don't refactor unless you have good automated test coverage (typically with unit tests). And if there are no test, write them before you start refactoring.

He notes that with successful unit tests in place, you can freely change the underlying structure of the application with (almost) no worries that your application will fall apart the next time it's run. He does point out the need for a bit of refactoring before the tests could really be successfully run (since there's a need for an external twitter connection).