Need help cleaning up my computer and optimizing performance

Hi there! I’m looking for someone to clean up my desktop and laptop, remove unnecessary files, organize folders, and optimize startup programs. I’d like a quick malware and cache sweep, update essential software, and set up a simple backup routine. Preference for clear explanations and tips so I can maintain the system myself. The work will involve both Windows and macOS (two devices), and I’d appreciate a practical, non-technical approach. Please confirm your approach, expected duration, and any prep I should do beforehand.