Sevencubed where does that number 2 links per 750 words comes from ?
Experience thru trial and error but I did add that your results may vary -- test test test.
...I don't repair watches I don't understand how it can help search engine...
I was only citing examples. Obviously you have to use keywords that support your primary focus -- rare is a keyword that does not have a supporting cast of characters.
That's where keyword research comes in. Know the supporting terms and apply them as well. Then in many instances you can also drill down on the secondary supporting terms and find their supporting cast members to the primary keyword actors.
How boring would a Broadway play be if you only had a star keyword without other colourful characters to add to the drama?!