In present-day SEO, you can't simply include as many keywords as possible to reach the people who are searching for you. In fact, this will actually hurt your website's SEO because search engines will recognize it as keyword stuffing -- or the act of including keywords specifically to rank for that keyword, rather than to answer a person's question.

Nowadays, you should use your keywords in your content in a way that doesn't feel unnatural or forced. There isn't a magic number -- it all depends on the length of your keyword and article -- but if you feel like you're forcing it, it's better to ignore it and continue writing naturally.