Keyword Distribution & Density
Keyword Phrases should be distributed into the human-readable content of the page, i.e. ‘on-page’.
Like with keywords in Page Title Elements, keyword phrases don’t have to appear as strict matches against the primary keyword phrase being optimised for. Thanks to advances made by Google’s algorithms they can have morphological (shape) variability and can also be matched-to by semantic (meaning) matches that completely different words in shape and sound (like company vs business).
This allows the content writer to be able to create better flowing content with the available keyword phrases for the page, without necessitating too much repetition of the exact same phrase.
Keyword phrases, whether they are morphological or semantic matches, should be scattered through many different sections of the page and utilize methods like fronting and tailing in paragraphs or sections. They may also utilize other highlighting methods like <em> and <strong> or be inside <h> and <a> HTML elements.
Read more about content and heading elements here.
Not all HTML highlighting elements are regarded equally. Keyword use inside a <h1> element has greater influence on SEO than the same keyword inside an <em> element. HTML elements containing keyword phrases with greatest to least influence may be something like this order: <h1>, <a> (inside <p>), <h2>, <h3>, <strong> (inside <p>), <h4>, <em> (inside <p>), <h5>, <h6>, <p>. While I have marked <p> as the least influential, the reality is that most of your keyword occurrences should be in <p>.
The power is cumulative.
Over-use of any element for ‘SEO purposes’ is not advised. Your content should be structured to appear best for your user. Usually overuse makes a page look messy or confusing, and this is negative for both UX and the Algorithm.
To explain the first two elements in my list a little differently, I’m saying that the main heading <h1> has the greatest SEO power if it includes the keyword phrase.
The next most powerful element in my view is the link anchor <a> from a different page to the one being optimised, i.e. links to a page optimised for “abc” should have link anchors that contain the phrase “abc”. Link anchors appearing on the same page as the content optimised for “abc” should contain the keyword phrases for their destination pages.
Another factor to consider with on-page keyword phrase use is the density of the keyword phrase in context, i.e. how many times per 1000 words the keyword phrase is used.
Here’s what Yoast SEO have to say about keyword density, saying that aiming for a keyword density of around 0.5-2.5% – that’s between 5 and 25 per 1000. Their SEO tool for WordPress is exceptional, but still has some traps.
The rule in my view should be: if the keyword use looks unnatural to me, then it looks unnatural to the Algorithm too.
So really what I’m saying is: there is no correct number per 1000 to aim for, but you do need to make the content mainly about the keyword you’re optimising for.
When you use an exact phrase too many times, it looks like you’re just trying to stuff your content full of phrases to gain rank. Well, that last bit might be your goal, but keyword stuffing is a bad idea. It has to read well.