SEO as a whole can be split into two different categories: on-page and off-page optimization techniques. On-page optimization is focused on everything you can do to boost your rankings directly on your webpage. Off-page SEO concerns aspects that function elsewhere, like backlink management.
Some might argue that on-page optimization has been weakened by Google updates that have sought to weed out pages using methods like keyword stuffing. While this is kind of true, it does not fully discredit on-page methods.
You can still take advantage of proper keyword usage, titles, and URL management, but as Matt Cutts puts it, “there’s diminishing returns.” Christian Arno from Search Engine Journal explains what still works in on-page optimization, and while some of the old techniques have been cut down, the most effective techniques are still tried and true.