wet your hair in the shower, and towel dry (leave it a little damp) get a medium to high hold mousse, about a handful or even more if your hair is long and thick, turn your hear upside down and use your hands and fingers to evenly distribute the mousse through your hair, scalp, ends, all of your hair!
then get a big scrunchie or hairclip/grip thingo and gather all your hair including fringe if you have one, to the very top of your head, scrunch it up into a messy ball and tie it up or clip it up so it stays that way. dont make it neat or a pony tail or a bun or anything, just scrunch it all to the top and secure it however you can. then go to bed (being right on the top of your head it shouldnt bother you at all) and in the morning take your hair out and run your fingers thru it to neaten it and you will have really really nice wavy beachy hair.using a curl enhancing mousse or spray while you scrunch will help intensify the look.
Enjoy your waves!
If you don't want to wait all night, try this:
Shampoo and condition your hair. Use a lightweight conditioner that won't weigh it down; try a volumizing formula.
Blow dry the roots of your hair with your head upside down, using the cool-shot button every few minutes to lock in some volume. Stop when your hair is damp, but not yet fully dry.
Spray some salt spray (also called sea spray, surf spray or beach spray) into your palms.
Run your palms over your hair, starting at the ends. Try not to get any directly on your roots.
Divide your hair into 7 to 8 sections (more if your hair is very thick).
Starting at the top of your head, twist each section into a loose bun and secure the ends with a bobby pin.
Repeat with the remaining sections of hair.
Allow your hair to finish drying while twisted up in the buns for 15 to 20 minutes.
Take out the bobby pins and finger-comb the waves into place, scrunching from the ends up.
Use a curling iron to fix pieces that didn't take shape well or give the front sections a more defined wave. To get a relaxed wave rather than a tight curl, don't open the clip on the curling iron. Just twist a piece of hair and manually wrap it around the barrel, holding the ends in place.
I have naturally wavy, thick, brown hair and it can sometimes be hard, if I can't style it right. Hope I help! :)