My hair now does this without the flatiron! - Waves in 15 minutes! Section hair into big sections then braid each in a loose braid. Run a flatiron over each braid, let them cool down, spray hairspray and undo the braids.
Separate the top half of the crown and section off the bottom into a ponytail. Next waterfall the top braid and section that off. Then tease the bottom half putting it into a low ponytail. Last combine the braid into the ponytail.
Another hair trick: How to do beachy waves in less than 5 minutes: Divide your hair into two parts. Twist each section and tie with a hair tie. Run your straighter/flat iron over both of the twist a few times. Untie twists, and you're done.