The core of Search Engine Optimization is writing good quality content that is tightly focused around a central idea.
This goes back to how we were taught to read and write. Jane and Mike had a ball. They bounced the ball. The ball was red. They were bouncing the ball and it hit a tree. – the whole story was about the ball.
Begin every new content creation project (new web page, description of your products, blog post, etc) by first determining what is the central idea. That is what is makes it the core of search engine optimization.
Then come up with the best terminology for that idea. You need to use the same term (keyword / phrase) on a consistent basis throughout your article.
From there write your article using what ever style that works for you (create outline, free write, etc). But keep in mind your central idea that is your keyword.
When your finished your article – take read through to see if you stayed on topic. Possibly look for unique ways to insert the keyword/phrase into the text of the article. Often you can replace pronouns with the keyword/phrase. (It bounced over Mike’s head >> The Ball bounced over Mike’s head).
There is no definitive answer to how many times the keyword/phrase should be in your content. More than once for sure, but do not make it hard to read. Some have said 2-3%, but that can get heavy on an individual term.
Next step to let the search engines know that you are trying to get at the core of search engine optimization and want your article ranked for those keywords is to use that keyword/phrase in certain key places that will show up on the webpage.
Be sure that the keyword/phrase is used in the webpage title and url.
It should also be used in an H1 (Heading1) tag on a website or in the post title of your blog.
And it should be used in your meta description.
Other good ways to really get to the core of search engine optimization is to highlight the keyword/phrase in bold, use it in a H2 (Heading2) tag, and/or use it in the alt tag of an image.
Let me know what you think the core of search engine optimization is if you do not agree with my advice.