Hi Raymond,
Keep in mind that you want to optimize a certain page for just one o two keywords. So with that idea, you shouldn't worry about the main keyword.
Im assuming that you're talking about you home page. For specific keywords, is advisable to have separate pages, a sort of landing page focused for that page.
Here some resources:
Begginer's guide - 5th chapter - Kw optimization
A Visual Guide to Keyword Targeting and On-Page SEO - Moz Blog
How to Optimize for Keywords in 2015 - SEW
On-Page Optimization for Keywords - Moz.com Academy
Hope I've helped.
Best luck.
GR.