There are people who say that you need keywords present all over your web pages in order to rank well. This is NOT true. Not only will this look strange to your reader it will also raise a red flag for Search Engines.
In fact, if you haphazardly insert keywords into your content you will most likely harm your rankings. The Search Engines are smart enough to read your text (in context) and notice that your keywords are out of context and do not make sense. Likely, the pages will be marked as spam and will not rank or worse be black-listed.
Instead of ‘sticking’ keywords into your content, aim to create themed pages and include only your keywords that best relate to the topic of the page. Instead of a precise rule of how to use the keywords aim for a natural flow and include variations of the keyword phrase and stem words that directly relate to and support your keyword phrase.