Depends on what you're building, of course, but seriously consider if what you're building is an MVP or not.

My most successful side-project has been the one where I didn't start out by using design patterns or TDD or fancy fun new languages as we do at my full-time job.

Instead, I spewed code vomit on the virtual floor of a tiny VPS, wrote most of it via SSH, and felt shame when users started using it because holy hell if they only knew what was underneath all that.

But ... that MVP generates income. Not quit-my-job income. But it's steady, and doesn't require a lot of changes. I plan on rebuilding it soon, as I need a better code base to handle upcoming plans. However, that embarrassingly messy hodgepodge has been running for a year, making money.

Good luck!