Here are three types of SEO you can focus on:

On-page SEO: This SEO focuses on the content that’s “on the page,” and how to optimize that content to help boost the website’s ranking for specific keywords.
Off-page SEO: This SEO focuses on the links that are directing to the website from elsewhere on the internet. The number of “backlinks,” and the publishers carrying those links, that link to your website help you build trust in the eyes of a search engine. This causes your website to rank higher as a result.
Technical SEO: This SEO focuses on a website’s architecture, examining the backend of that website to see how each webpage is “technically” set up. Google cares as much about the code of a website as it does its content, making this speciality quite important to a website’s search engine ranking.

Source: https://blog.hubspot.com/marketing/seo-strategy