Learn to use commas correctly. Comma usage is too complicated to explain here, but be aware that they not only affect readability, but reflect your skill as a writer. Read your work out loud, if necessary, to help you figure out where they’re needed.  Their primary purpose is to separate sentence elements with a slight pause to provide clarity. Hint: You’ll often need one before “but” or “which”. Oxford commas, where you include a comma before the “and” in a series of items, is often used as well. For example, “Her favorite foods included pizza, spaghetti, chocolate, enchiladas, and fajitas.” Without the Oxford comma, “enchiladas and fajitas” could be considered to be a reference to a combination plate as opposed to separate items.