A messy start to a project rarely fixes itself later — it just resurfaces at a worse time, usually right before a deadline. A short onboarding checklist fixes most of that before it becomes a problem.
Before any work begins: confirm the point of contact on the client's side, agree on how often you'll check in, and get access to whatever accounts or files the project actually needs — not after you hit a wall two weeks in.
In the first working session, walk through the scope together out loud, even if it's already written down. It's the fastest way to catch a misunderstanding while it's still cheap to fix.