On which you focus on will depend on what you run.
In the past I was involved in commercial sites; and initially there was a big focus on keyword research, used to create good titles that will work. This was then used to produce copy repleat with keywords to soak up as much and as broad of search as possible.
However, once that was done, there was then a much bigger, in terms of £/time, on off-site. I left the SEO scene at about the time in which Google began a massive and on-going clean up that made a lot of the old gutter link building techniques damaging or risky. I don't really know what link building techniques people use for your average commercial site these days. After I left the scene there was a big shift to more acceptable link building techniques like guest blogging, solely for the purpose of link building. It seems this has no become a pretty grey area.
Most of the people I knew that were involved in SEO have been washed away and many of those who are left have had to seriously change their game.
On the other hand, if your site is non-commercial or has a non-commercial component, like a popular industry blog attached to your site, then I would pay little attention to SEO.
I run a non-commercial site and in coming up to four years I've spent maybe 8 hours link building near the beginning. I've never spent any time keyword researching and the on-page is educated best-guesses. The reason being is the success of the site is the content getting links on its own in combination with 10s of million words of text soaking up predominantly long-tails. Its only in the last year the site has started to rank for broad, head terms.
If you have a commercial site, like selling gifts of kitchen sinks, very few people will link to it unless there is something in it for them. So off-site becomes so much more important to focus on. What people do these days though I have no idea.