My way of using keywords while writing is extremely simple.

All I do is write 1 main keywords and two secondary keywords anywhere like notepad or Ms word. Apart from this I also make sure that I have used Google auto suggest as well as LSI keywords while writing.

This makes my job even easier as I mixed up natural keywords and my main keyword. At the meantime LSI keywords, long tail keywords also comes very handy.

You can also use “People also ask” section where you will se multiple questions. You can use those questions in your content and answer them as well to make your content unique and valuable.