Catalog of Refactorings by Martin Fowler: https://refactoring.com/catalog/
Start cleaning your Legacy codebase with The Daily Refactoring Hour: https://understandlegacycode.com/blog/start-cleaning-legacy-with-daily-refactoring-hour/
Refactoring is a daily job: https://www.briansnotes.io/article/refactoring-is-a-daily-job/
How to create a culture of continuously refactoring code? https://medium.com/meliopayments/how-to-create-a-culture-of-continuously-refactoring-code-752ff69c8c74