Don't Get A Haircut
It seems obvious, but to get the proper surfer look, you'll need enough hair to pull it off and this means growing your hair out. You'll want the hair to be long enough to just come down to the eyes in front and to the bottom of the ears on the sides. Prepare yourself for that awkward stage where the you can't do anything with your hair -- at some point it will become too long to style, but still be too short to, uh, style. You'll just have to be patient through this stage of growing it out.
Get A Haircut
The perfect surfer hair starts with a great shag haircut. For this type of style, the hair is cut in long layers all over the head. When doing a shag, I almost never pick up a pair of shears -- these haircuts work best with done with a razor (no blunt shear cutting here). The razor cutting technique gives the hair movement and separation and provides that "deconstructed" look around the edges. When you go in for the cut, you'll want to take a photo with you -- find a picture of a shag haircut on a model who has hair similar to yours and take it with you.
For styling a long shag, if you're going for the beachy look, towel dry the hair, but don't dry it completely. Next, you'll want to choose a matte finish product such as Hanz de Fuko Quicksand or Bumble and Bumble Surf Spray (available at salons and online). These products are salt infused and will give your hair that sun-dried, wind blown feel with a matte finish. Work the product through damp hair and let it dry naturally (or if you're in a hurry you can use a blow dryer with a diffuser (one of those big blow looking things with fingers in it).
I really like the surfer type style for its versatility. The style can, of course, be worn shaken out and shaggy, but you can also add some shine product (such as a pomade) and wear it brushed back out of the face for a more formal look (if it's long enough, you can tuck it behind the ears as Brad Pitt has been known to do). Naturally the surfer style is much easier to pull off if you leave near the beach, but it can work for those of us who are landlocked as well.
If you want to go the extra mile, you can also seek out a professional colorist and have some natural highlights added to give the hair that "sun kissed" look. Of course, spending a lot of time in the sun will also do that, but make sure you use sunscreen. If your hair is stick straight, you can also have your stylist add a permanent wave to the hair. You can achieve a similar, temporary result at home by scrunching the hair with a blow dryer, but that will add a bit more work to your morning routine. Just keep in mind these processes are permanent and can damage the hair, so you ONLY want to have them done by a professional.
To maintain a healthy look for longer hair, I recommend shampooing and conditioning daily, drying carefully (always pat the hair dry instead of rubbing it with a towel), using a wide tooth comb or brush and avoiding damaged caused by pool water.
Once you get the surfer look, throw on some SPF and a pair of board shorts and hit the surf!