There are several things that you need to take into account whenever you’re SEO optimising your site. Although the importance of all of them is not the same all of them need to be taken care and if you’d asked me I would say there a few more to consider as well.
The order that I would suggest to focus on would be like this:
- Content
- Structure
- Settings
- Code
- Everything else
Like I said this is a very broad response and SEO requires a whole plan and strategy behind but hopefully this will put you in the right track.