It sounds like you are talking about the meta description tag. There are other meta tags too.
Write them compelling and be sure to use your important search phrases at the beginning of the tag. But don’t just list them, write your meta description like it’s a 2 line summary of the page, with keywords inserted. CTA also can help (IE click here to find out more).
There’s still no guarantee that G will use the description, but without it you are at the mercy of Google’s own (terrible) snippet generation.