Theres a lot of debate online about the optimal keyword density, proximity, frequency, plurality, objectivity etc. One principle worth keeping in your conscious is the following:

“A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts.”

Keeping it simple: Content should flow naturally with descriptive keyphrases/words prominent.

I’ll look as specific ways to draw emphasis on keywords/phrases in later posts.