Structural mark-up of the HTML pages, much too many peoples dismay, and people will continue to deny this, is a very important aspect of SEO. What is structural mark-up, it is the structure of the HTML elements on the web page and how they outline the content that is contained on the page. That is how those crazy crawlers know how to format your content for searching.
Of course keywords, competition, content and hundreds of other factors make up a SEO ranking, but structural mark-up is one of the very first things looked at by the crawlers. And it is extremely important. Why do I point this out. Because the structural content of most WordPress sites is absolutely terrible. Just look behind the page at the source of those pages, and you will see exactly what I mean.
It is not the fault of WordPress, WordPress is a one-size-fits-all IDE. It was meant for Blogs and in that aspect it is pretty good, but it was never meant to be a serious contender in SEO. All those little plugins, just make it worse they add more and more crap to the structural content.
With the amount of websites that are currently out there it is very difficult, even with perfect pages, to rank high quickly on the search engines. That is just not a realistic expectation. Especially with sites like Amazon, eBay and the numerous eCommerce sites that have registered and work 10's of thousands of keywords. They spend millions of dollars a year making certain that they stay in the top 5 listing, normal people cant compete with that type of marketing. And you can be pretty certain that they have some of your keywords in use.
Do the things you can do to help your site rank. Keep your markup clean and structurally correct, have good quality back links to your site, that takes time, have good and fresh content on your site that is of interest to an audience, promote your site through social media, and relevant sites, and be patient. It takes time.
Traffic plays a part in SEO, the more popular the URL, the more often you are crawled, and going to your site over and over is not going to increase your popularity. The search engines are smart enough to track the source of the traffic. One of the things I never hear mentioned when people discuss SEO is the age of the URL. That also plays a role in SEO, not a high importance role, but a role, every little bit helps.
The key for all of the this..... read some of the content on the W3C and IETF on how pages should be structured for the web, remember that is the governing body that makes the standards for the world wide web. The search engines follow those standards and add their own algorithms and parameters for determining SEO rankings. SEO is a constantly moving target, and for good reason. They are trying to keep people honest....
It is not that hard to follow, but you are not going to find it in a package or a plugin.