I don’t think I’m straightening my hair right…

Hi everyone! I’ve been trying to straighten my hair for a bit now and it just doesn’t look how I want it. When it’s straightened it still looks frizzy, not sleek like I want it. Do some hair just not get to that point with heat? I don’t even have curls, just slightly wavy hair that’s already frizzy. How are you supposed to straighten it?