It goes without saying that less popular keywords will have less competition in the search engines. Therefore, it is always a good idea to sprinkle a few uncommon keywords and synonyms in your main body text.
It is vital that you include keywords that maybe less popular than the main keyword you are targeting.
The reason is that if someone searches for a particular keyword phrase and the keywords do not appear in your webpage, a search engine is unlikely to consider it as relevant for the search query. The search engine is much more likely to rank another webpage which does include all of the search keywords higher than yours.
For example, Google state that they only return webpages that contain all the words in a search query.
Keyword frequency refers to the number of times a keyword, or keyword phrase, appears within a page. The theory is that the more times a keyword or keyword phrase appears within a page, the more relevant the page is for that keyword. But do not overdo it, by plastering a webpage with the targeted keyword. Search engines frown upon keyword spamming.
Keyword density is the ratio of targeted keywords contained within the total number of indexable words within a page.
For example, if a page has 100 words in total and of those 100 words 3 words are your targeted keywords, then the keyword ratio is 3% (3 divided by 100).
In general, I suggest using a keyword density ratio in the range of 1-3%. For specific search engines, it depends on which search engine you are targeting, as different search engines have different preferences regarding keyword density.
You can determine your page's keyword density using the following procedure:
The program will search for your keyword phrase entered in the “Find” input box and replace it with the keyword phrase in the “Replace” input box, which in our case will be the same. It will tell you how many times the keyword has been replaced..
Note: The above procedure is a very basic method of determining the keyword density of a page. The problem is that there is no standard way to calculate keyword density for all search engines.
Factors such as stop words, word stemming, and whether keywords in a particular HTML tag are indexed all affect the total number of indexable words that a particular search engine would end up with.
For a quicker method of calculating keyword density try this online tool, "Keyword Density.”