Starting from scratch and learning what not to do (I will not promote)

Basically, the title. I'm diving into entrepreneurship while still holding down my 9-to-5. Since time is limited, I want to make every step count by learning from those who have already navigated this path. Instead of reinventing the wheel (or making unnecessary mistakes), I’d love to hear insights from experienced entrepreneurs, especially on what not to do. I know that some lessons only come through experience, but if I can sidestep common pitfalls early on, I’ll have a much better chance at building something sustainable. Whether it’s avoiding bad business decisions, managing time effectively, or staying focused on what truly matters, any advice, big or small, is more than welcome. Please don’t hold back, even the most obvious tips might be high insight for someone just getting started. I truly appreciate any wisdom you’re willing to share.