A look into the past and present
On-page optimization: When performing on-page optimization in the old days, SEOs would map two to five keywords per URL and optimize the page elements (title, meta description, headings, body content and so on) for these keywords.
But things have changed.
Now, with advances in semantic search and machine learning, a page can rank for a lot of related keywords, not just the keywords for which you optimize the page.
This is a better way of doing things, as having content that fulfills the needs of what users are looking for (rather than just being the best match for a given keyword string) is a better experience.
Modern-day SEOs should have a solid understanding of not just content creation, but also content promotion.
Whereas previously it was all about optimizing existing landing pages based on search volume and striking distance, SEO today is a mixture of optimizing existing content and creating, optimizing and amplifying new content that meets end-users’ needs to enforce your brand and capture social signals and links to rank higher in the SERPs.
Back in the day, it was all about optimizing for desktops because that was the primary device used to surf the web.
Today, mobile devices have quickly become the way that people consume content.
While the desktop is still relevant, digital media consumption on mobile devices has skyrocketed in the past several years and will continue to grow.
According to comScore, mobile now consists of 65 percent of digital media time.
Additionally, in 2015, mobile officially surpassed desktop in terms of Google searches performed.
SEOs must focus on optimizing the mobile experience, particularly apps, and making sure that mobile pages load within two seconds.
Google has changed its local results so many times during the past several years — from the 10-pack to 7-packs, and now the 3-pack.
In the old days of local SEO, it was easy to spam the listings by incorporating keywords into the business name, getting links from spammy directories, fudging the exact location of the business and so forth.
Now, local is all about positive reviews and (thanks to the Pigeon update) some of the more traditional ranking signals like relevance and page content.
Source: The evolution of SEO