Step #6: Now it all depends on how small or big you want to wavy hair to be. According to that, get the iron to transform your straight hair wavy. If you don't want to curl your hair completely, just get a large iron that will get the job done. You will hold each sections of hair on the iron for your preferred end result. Once all the sections are taken care of, slightly fluff your hair so that all the curls set in place and don't look closely fitted.