Ask HN: How do I apply for Y Combinator well?

I have 8 years of software developer experience. I took the founders course and was going to do a submission of some past work for YC2022 just to see what would happen. However I stopped short of that because it doesn't seem to be my best work, it doesn't have a large user problem, and it is just a "broken toy" thing.

I would like to figure out what I can do to find a problem first, but I'm not sure of where to look. The cool idea I have for music publishing related startup just has a book reference, no users involved yet :\. tl;dr : What can I do so I will be ready for YC 2023 Fall and submit something decent?