Serious Question: Common Pitfalls for New Founders I Should Avoid?

Hey everyone, I'm Megan, a Script Supervisor usually focused on timing and continuity, but I'm trying to launch a small side venture helping indie filmmakers with pre-production planning and scheduling. I've got a decent grasp on what I need to do to get started (registering a name, figuring out services) but I'm pretty green on the 'business' side of things. I've already heard whispers about the dangers of verbal agreements, or hiring people before you absolutely need them, or worse, forgetting about permits altogether. It's a bit overwhelming. From your experience, what are some of the most devastating, yet common, pitfalls you've seen new founders fall into that someone like me should be actively trying to avoid from day one?