According to deep website investigation, most of the websites ranked #1 on Google use keyword as follow:
2% main keyword (online SEO)
25% related LSI keywords (optimize online SEO, cool online SEO site)
40% URL as anchor text (create image links and hyperlink images)
23% generic keywords (random keywords like: click here for info on online SEO, More information on online SEO, Click here for more online SEO information, Website full of online SEO information is here. These are used them within the articles which makes more sense.
10% coming from website title
Total of 100%