Google has updated their document on local ranking help and posted about it in their features updates page for Google My Business.
The content has been increased by almost three times of the earlier existing content and the old content has been revamped.
The document says:
“Can’t find your business? Improve your info.
You may find that your business doesn’t appear for relevant searches in your area. To maximize how often your customers see your business in local search results, complete the following tasks in Google My Business. Providing and updating business information in Google My Business can help your business’s local ranking on Google and enhance your presence in Search and Maps.
Enter complete data
Local results favor the most relevant results for each search, and businesses with complete and accurate information are easier to match with the right searches. Make sure that you’ve entered all of your business information in Google My Business, so customers know more about what you do, where you are, and when they can visit you. Provide information like (but not limited to) your physical address, phone number, and category. Make sure to keep this information updated as your business changes. Learn how to edit your business information
Verify your business locations to give them the best opportunity to appear for users across Google products, like Maps and Search. Learn more about verification
Entering and updating your opening hours, including special hours for holidays and special events, lets potential customers know when you’re available and gives them confidence that when they travel to your location, it will be open. Learn how to edit your hours
Interact with customers by responding to reviews that they leave about your business. Responding to reviews shows that you value your customers and the feedback that they leave about your business. High-quality, positive reviews from your customers will improve your business’s visibility and increase the likelihood that a potential customer will visit your location. Learn more
Adding photos to your listings shows people your goods and services, and can help you tell the story of your business. Accurate and appealing pictures may also show potential customers that your business offers what they’re searching for. Learn more
How Google determines local ranking
Local results are based primarily on relevance, distance, and prominence. These factors are combined to help find the best match for your search. For example, Google algorithms might decide that a business that's farther away from your location is more likely to have what you're looking for than a business that's closer, and therefore rank it higher in local results.
Relevance refers to how well a local listing matches what someone is searching for. Adding complete and detailed business information can help Google better understand your business and match your listing to relevant searches.
Just like it sounds–how far is each potential search result from the location term used in a search? If a user doesn't specify a location in their search, Google will calculate distance based on what’s known about their location.
Prominence refers to how well-known a business is. Some places are more prominent in the offline world, and search results try to reflect this in local ranking. For example, famous museums, landmark hotels, or well-known store brands that are familiar to many people are also likely to be prominent in local search results.
Prominence is also based on information that Google has about a business from across the web (like links, articles, and directories). Google review count and score are factored into local search ranking: more reviews and positive ratings will probably improve a business's local ranking. Your position in web results is also a factor, so SEO best practices also apply to local search optimization.
There's no way to request or pay for a better local ranking on Google. We do our best to keep the details of the search algorithm confidential to make the ranking system as fair as possible for everyone.”