On Page SEO Includes
1 - Meta Tags Optimisation ( Acc. to Keywords )
2 - Content Optimisation ( Fresh and Unique Content )
3 - Images and videos Optimisation ( Alt Tags )
4 - Keywords Placement acc. to their density
these are just basic and top most things
Basically making the site SEARCH ENGINES and USERS friendly. So, that search engines can crawl your website and user can easily read or buy products from your website. Good Luck
If you want on page optimization that will help you for the LONG-TERM, I am your guy.