The single field with the most influence is the primary category: it decides which queries you are eligible for at all. Secondary categories extend reach without diluting the primary one, provided they match services you genuinely deliver. After category come accurate hours including public holidays, the service area, attributes, photos and an up-to-date services list.
The recurring failures are mundane: keywords stuffed into the business name (a reportable violation competitors do report), duplicate listings created by former staff, unmanaged public edits, and an account owned by someone who left the company two years ago. Keep the profile in the company's name, assign an owner, and review it monthly.