To achieve a high ranking in the Google 3 Pack you need to have keyword category pages on the main website that match keyword categories on the Google My Business listing. This is a Google Maps 3 Pack indicator, not a traditional SEO strategy that should be implemented.
There is a systematic process to create a highly functioning Google My Business account. If you don't match your main website and your Google My Business account there is a high probability that your business will not rank highly in Google Maps. Google Maps 3 Pack listing is the most effective way to get calls and leads for any business. In mobile search on Google, there is no link to a website only a call link, with 90% of all searches being performed online, having your business in the Google Maps 3 Pack is a high-value goal.
Google offers a website builder that helps with rankings and SEO. This website will feature Google Posts, Google Reviews, and other Google My Business information with contact information.
I would highly recommend a Blogger page with relevant content about your business services that link back to the main website home page.
Having an active YouTube account is a great way to promote any business to inform potential customers about the business. The advertising revenue potential is also very valueable.
A technical function is required to have the you main website listed on Google and to be found by all the major search engines.
Google experts say that having an active Google Ads account with advertising spending has no correlation to website rankings, however, I recommend that there is always a Google Ad running, even if it is small. Traffic always helps website rankings.
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Create an online review process for your business to dramatically improve online review creation, management & marketing for increasing more online reviews, managing good and bad reviews, using good reviews for marketing on Social Media.