First, get yourself a few thin hairbands, and split your hair into small parts. The more plaits you do, the smaller the waves will be, and the more volume you will achieve. For larger waves just do two or three.
Plait your hair :)
Leave your hair for a while, the best thing to do is do this in the evening. You will wake up with beautiful fresh looking hair, which will last for at least 2 days.
This step is optional : If you have left a large enough gap of hair at the ends, straighten them. This gives a more tasseled, beachy look to your style. I personally love beach hair.
Then just undo the bands and let your hair go! I would recommend NOT to brush or comb through your waves, as this will ruin the textured look of it. Run a bit of Argon oil or my personal favorite, baby oil through the ends and your ready to rumble.
Try it out yourself and let me know how it goes!