Keyphrases are two or more words put together to form a keyphrase (long tail keyword), such phrases are usually much easier to optimize then the individual keywords, because single keywords usually have higher competition.
The main keyword or keyphrase should be mentioned in the title, URL, and repeated in the article-heading of the page, as well as in the content. You can also include it in the meta description of the page.
Keyword and keyphrase analysis and density
The keyword density has little to do with how a page ranks. Of cause you should mention the keyword, or keyphrase at least a few times throughout your content, but anything beyond that is likely to have a negative effect. The main keyword or Keyphrase should as minimum be mentioned in the title, and repeated in the article-heading and content of the page.
There are many factors which determines how a page should rank, and one of the hardest to overcome is competing pages. While the density of keywords can impact you negatively, it has little to do with competing sites that are simply outranking you.
Some of these sites are well established, have many incoming links, and higher authority to help them achieve better rankings. Their individual pages might not have that many links, but authority can also flow from the main domain to deeper pages, (given that they are linked internally.).
Say you where to find a keyphrase often used by searchers, like "very unique keyphrase", and there where no pages with that exact match, then you may very well be able to get a top 5 ranking spot, if you were to write an article mentioning this exact keyphrase. However, often there is a lot of competition preventing this, because the topic itself might not be unique enough, or your authority is not yet high enough to get good rankings on the topic.
Uniqueness of content
The uniqueness of your content is something which is far more important then keyword density. If one of your pages does not rank high enough for certain search phrases, then try to look into what you can do to improve the content of the page. One way to do that, is to change a non-matching title, to a title that includes the keyword or keyphrase used by searchers.
Also, try to cover more subjects to make your content appear more unique, as they say: content is king. Covering multiple closely related subject on the same page, is likely to increase the uniqueness of your content a lot.
Many online shops do not understand this. So their individual product pages might not even rank on the first page at all, while often they could achieve a top 10 placement with just a little effort put into writing longer content.
Think about the keyphrases on your page
Keyphrases, or so called long-tail keywords are far more important then individual keywords. Have you actually included the phrases on your page that people would be using when searching? A lot of website owners totally overlook this, making their sites perform really bad in the search engines.
Think about the phrases that you use on the site, for instance, if people are searching for "SEO Tutorial" to find the SEO Tutorial on Beamtic, then it would be a good idea for us to include the phrase somewhere in the content on that page.
Some webmasters also include "lists" of phrases and words on their pages. Do not do this. It's useless to your users, and will just make your pages appear more spammy. Instead try to include potential search phrases more naturally, in a way that its also useful for users. If a site looks like spam to a user, they will also be less likely to link to the site.
Compare your content to competitors
It can also be useful to compare Competing pages, with the pages on your own site. I.e. Do the competing pages include actual keyphrases? If they do not, then you could sometimes easily outrank them by simply including keyphrases on your own pages.
You could also check to see if your competitors have exact title matches for their pages, which often is not the case. Simply changing your page titles to exact matches to certain keyphrases can sometimes give your pages a boost.
It may also be somewhat beneficial to include the main keyword or keyphrase in the description meta tag.