It depends on your roadmap, I know typical consulting answer.
Not with a random list of unused Fields, Not with a generic best practice checklist.
Your cleanup should start with one simple question: what do you want to achieve in the next 3 to 12 months? Cleanup is not the goal, it's the enabler.
If your roadmap calls for a new sales process, cleanup should help you roll it out faster. If you're improving Service Cloud, cleanup should help agents close cases more reliably. If Agentforce is on the horizon, cleanup should make sure your data, processes, and user experience are ready to support it.
Depending on your roadmap, cleanup can mean very different things. It might mean deleting unused Page Layouts, Fields, Reports, and List Views. It might mean simplifying Record Types or security. It might mean removing old Automation, or even ripping out a Trigger Framework that no longer serves the purpose it was built for.
There are many roads to Rome, but the one you choose should depend on where your business is actually trying to go.
Cleanup should help you deliver your roadmap faster, cheaper, and more reliably. Everything else is just housekeeping.
Book a free 60-minute Salesforce Technical Debt Audit: a score for Usability and Build Quality, and your top cleanup priorities.