Add expiration dates to TODO comments
When I spot an idea for a non-trivial refactoring, I often add a TODO comment. The ideas which are not acted upon immediately are often, but not always, valuable. A problem is, that they tend to pile up without being resolved. In a mid-sized real-world code base that I maintain the ratio was roughly one such comment per 100 SLOC.
Therefore I decided to add a reasonable explicit expiration date to any such TODO (some 4 to 8 weeks in the future). When I encounter a comment that has expired, deleting it is a perfectly viable cleanup. The code structure obviously was not so bad after all, or else I would have put energy into the refactoring already.