The most effective approach to SEO is to target only one keyword phrase for each page. For example, if you have a page about tacos, don't talk about burritos on that page as well. Burritos should have its own page.
"One page per topic is almost always the best strategy."
A well optimized page will rank for many related keywords
When you follow POP's advice to optimize your page for your main keyword phrase, you will often find that your page ranks well on Google for many related keywords. If your main keyword is "tacos recipes", for example, your page could easily rank for "homemade tacos recipes" and "easy tacos recipes". Well optimized pages can rank for many keywords.