What Are Some Good Practice Paradigms For Your Old Codebases?

I've been coding for a long while now, but I've probably 6-8 projects that I've more or less finished.<br><br>I want to practice with these, but I don't know what aspects to practice. I'm mostly a python programmer, but for the sake of argument, let's say I'm proficient in python, git, bash, and Jupyter notebooks.<br><br>What paradigms do you use to practice with your own old codebases?<br><br>What are some good ones you've used before?