Here's my experience from the last ~12 years as a full time solo developer:
1. I use Github issues to track features and bugs that I am working on. It's useful because sometimes I come back to a feature months (or even years) later, and I don't have to start from zero again.
2. I've tried a lot of systems for planning work, but I found nothing that beats pencil and paper. Plans always change anyway, it's good to just spend 5-10 minutes planning your day before you start working.
3. It doesn't matter if you move back and forth, change priorities, etc, as long as you keep making progress. You only find out after the fact which of the features were the ones that really made a difference.
4. At some point I realise that I'm getting close to a release, then I switch into "release mode", I stop working on new features and just fix bugs until the release is done.