Keywords or Keyphrases are the terms we want to target on our page. Firstly, think about your message and what terms prospective readers might enter into a search engine. Those are some good starting candidates for keywords.
Many other factors contribute toward determining what keywords we want to target, including competition, popularity, and relevance. For instance, if we were optimizing a site for a company that sells life insurance, the keyphrase "Life Insurance" might seem like an obvious choice because it has high relevance to the service we offer. However, a search in Google for the term yields in excess of 1,000,000,000 results. To compete with that many sites, we are going to have to spend an enormous amount of resources to be successful.
Responsive, Mobile-optimized Design for SEO
Google's proclamation of Mobilegeddon caused trepidation in even the most stalwart SEO experts and website owners. In short, Google lead the charge on Search Engines giving SEO preference to sites that were optimized for mobile viewing. So if your website isn't of Responsive Design and your competitor's equally good site is, guess who gets a higher pagerank with Google. (Hint: It's your competitor!)
Check if your site is considered mobile-friendly with Google's own Mobile-Friendly Test web tool. If your web developer does a good job, you will get a great report like this:
Markup and Meta Data
Not only does complying with proper coding standards cause your site to render and function better, but it is an integral part of good, affordable search engine optimization. Good code will help the search engines see that our content is the type of stuff our readers would want to find. Good, clean code also translates directly to page-load speed. Search engines love fast-loading pages. Therefore your site will get better search results.
There is no doubt that "good links" add to the searchability of a site. But as with most items in life, too much of a good thing can be a bad thing. There is as much art as there is science to competent SEO. There are no hard rules for anything in the world of SEO because Search Engines closely guard their algorithms and policies better than most independent governments do their wealth. So knowing how many links are optimal for your site requires the gentle vision of a nuanced SEO artist. There are also types and aspects of links to consider. Backlinks, outbound links, internal links, anchor text are just a few elements to consider.