At Flock, we talked about scheduling some kind of regular technical-debt-fighting week to happen every so often - some period of time where we don't do any new features (and even try to de-prioritize interrupt-driven stuff) and focus on shoring up, cleaning up, tightening the bolts, etc.

Here are some things broadly to think about:

• Add unit tests where there are none. Increase "code coverage".
• Write docs (and make diagrams!) where there are none.
• Reduce code duplication, and increase code re-use where appropriate.
• Break up ultra long methods, classes, and files into more understandable chunks.
• Remove half-implemented features!
• Remove dead code!!
• Add comments where there are none, and correct inaccurate comments.
• Deal with the existential questions facing the code that none of us wants to touch.
• Increase happiness and general zest for life.