Whether you perform local SEO for yourself or your clients, or you are a web designer, Google has created vital documents that you need to read, understand, and implement.
https://webmasters.googleblog.com/2018/05/helping-webmasters-and-content.html
There are a couple documents in this list that are especially helpful. One is the Google Webmaster Guidelines. The other is the SEO starter guide. When I have people call me and ask about starting out in SEO, these are the documents that I tell them to read first.
