This looks like the messy beach hair that I am totally envious of. So pretty. And even better--- SO EASY to achieve. You are going to start by straightening the hair nice and flat. You don't want to skip that step even if you have straight hair that you are working with. Flat ironing just gives it a pin straight look that I love.
Next you twist up most of the hair leaving only a small amount out on the bottom and curl some spirals in the hair. Or if you have a crimping iron you can crimp the hair. That would be way fun. After you have some curled you divide and drop down a little more and do it again. Keep doing this until you get to the very top. That way you just have some fun curls peeking out through all the straight hair. Having the hair down doesn't mean you can't have a little style too it. This is a good way to still have style with a down do.