Every time you look up something on StackOverflow, refer to the API docs, or refer back to the ticket, use case, or requirements document, make a note of your question and the answer. Even when you just stop typing to take a break, note down where you are and what you just did.

Every time you think you need a TODO comment, make a note instead, or also.

Consider Kent’s Beck’s recommendation to write down every decision you make.

Some other views

https://shannoncrabill.com/blog/taking-notes-as-a-developer/

https://blogs.oracle.com/javamagazine/post/take-notes-as-you...