Title tag, 15–65 characters The blue headline in Google results and the text in the browser tab.
Mobile viewport declared Without this line phones render your site zoomed out and unreadable. Most of your customers are on a phone.
Structured data (JSON-LD or microdata) Machine-readable facts - address, phone, hours. This is what puts a business in a map card instead of a plain link.
At least 300 words on the page A page with almost no words gives search engines nothing to match a search against.