For on-page optimization the most important factor is to focus your title tag on keyword.
The next ones will be:
- High quality text (long enough) including your desired keyword
- H1 and other headings optimized
- A lot of images/videos (with alt attributes)
That is the most important, but there are a lot more of relevant factors which may help. Like contextual links to relevant pages/sites, clean html code, Also, some sitewide issues can harm your onpage, like too many outbound links on page, or duplicated links, not good website structure, cannonical problems etc etc...
But if you have a good quality content it means a lot. I have a website in wordpress and didn't do any SEO and it is getting like 3000 unique per month for around 20 posts. But posts are pretty long, informative and full of images and videos.