The category, which is the most important field
The primary category is by some distance the field that most influences which searches you appear for, and it is also the one most people get wrong by trying to cover everything. A bar that serves food and picks "Restaurant" is competing in a different league than if it picks "Tapas bar", and the second probably describes better what people are searching for when they search for it.
Pick the primary category that describes what you do most of the time, and use secondary ones for the rest. Do not add ten secondaries: they dilute rather than add.
Address or service area, not half of each
If customers come to your premises, give the exact address and make sure the map pin lands on the door rather than in the middle of the block. If you go to them — a plumber, an electrician, a mobile service — set it up as a service-area business and hide the address, which is probably your home.
And the detail almost nobody checks: name, address and phone have to be written identically here, on your website, on Apple Maps and in any directory you appear in. "C/ Mallorca 12" in one place and "Carrer de Mallorca, 12" in another are two different businesses to a search engine that is not sure.
The things that go stale
A profile is not finished; it is maintained. Three things go stale and quietly sink a profile when nobody touches them.
Holiday hours are the first and the worst: a customer who arrives at a locked door because Google said you were open leaves a one-star review that will cost you months. Photographs are the second; a profile with four-year-old photos says something without meaning to. And the "Questions and answers" section is the third: you can answer them yourself, and if you do not, anybody can.
Reviews: asking without getting into trouble
Asking satisfied customers for reviews is legitimate and it works. What is not legitimate is filtering: asking only the people you know are happy, offering something in return, or writing them yourself. Besides breaching Google’s policies, displaying ratings without explaining how you verify they come from real customers is an unfair practice under Spanish consumer law.
The practical version: a short link to your profile, asked for at the moment the customer is pleased, over the channel you already talk to them on. And replying to all of them, the good ones included, in two lines and without a template.