SEO can be split up into two separate categories; On-Page SEO & Off-Page SEO.
On-Page SEO refers to all the things that you can do ON your website to help you rank higher, such as page titles, internal linking, meta tags & descriptions, etc.
On-Page Search Engine Optimization factors:
1. Page Titles
2. Meta Descriptions
3. Meta Tags
4. URL Structure
5. Body Tags (H1, H2, H3, H4, etc.)
6. Keyword Density
7. Internal Linking
Hope this helps you.