Ars Technica has a summary of Stack Exchange responses to the question:

I’m working on a project solo and have to maintain my own code. Usually code review should be done by someone other than the author so the reviewer can look at the code with the fresh eyes. I don’t have such luxury. What practices can I employ to more effectively review my own code?

There are some good suggestions listed for what I think is a common situation, e.g., scientists developing code for their own use.

Of course, I would recommend writing some unit tests as well.