A wonderful thing about windsurfing is that there is always something new to learn; you have just scratched the surface. So you might ask, where can you go from here to learn more? There are numerous paths for continuing to learn and improve.
Learn Free Style Tricks
Learn a few acrobatic tricks on your board. There are at least three reasons for learning some of these tricks: (1) Free style tricks help you get a better feel for your board and rig; (2) Some free style maneuvers become important in later sailing (e.g., water start, sailing clew first, duck jibe); (3) It's fun and looks cool. It used to be that nearly every sailor practiced these tricks. Some of these free style tricks are listed at the end of this section (Free Style).
Buy a harness
If you have got this far, you are no longer a beginner! Celebrate by buying yourself a present: a harness. Let me sing the praises of the harness.
With a harness, your arms will not get tired. You will be able to extend your time on the water. You will go faster in high wind because you will not get knocked about with every change in wind speed and you will be able to hold down the sail with your body weight. As you go faster, the strain on your rig and you will be less because more of the board will be out of the water and therefore have less drag. Finally, you will be able put downward pressure on the boom which will transfer through the mast to the board. This downward pressure will hold the nose of the board down enabling you to move back on the board to the footstraps. When you get back in this position you will go very fast.
There are three kinds of harnesses on the market: chest harnesses, waist harnesses, and seat harnesses. Most sailors use a seat harness ($40 to $60). Chest harnesses are often used by wave sailors who have to hook in and out of the harness frequently. Seat harnesses are most often used by slalom sailors (you) who want to go fast in relatively flat water. (These preferences may be changing.) Do not buy an inexpensive waist harness; they usually ride up and become an ill-fitting chest harness.
Where to go for more instruction
Other sailors are your first resource for learning more about windsurfing. Windsurfers are a very affable group, and love to talk about their sport. Do not feel shy about asking help from another sailor. Get to know the other sailors in your area. Our advice, however, is don't ask your questions to a sailor who is racing to rig on the first windy day in a month.
If you picked the right windsurfing school, they will have intermediate lessons for you.
There are numerous instructional videos on advanced skills such as water starting. We have already mentioned the book Beginner's Guide to Zen and the Art of Windsurfing, by Frank Fox (Amberco Press). For these, check your local shop.
Windsurfing magazines are a good source on information. In the United States, Wind Surfing magazine (800-394-6006) has articles and instructional hints for every level of skill. There is also information about clinics and windsurfing vacation spots (see below). If you read German, the magazine Surf is reported to be excellent.
There are several traveling instructional clinics that are a great way of learning more. The clinics last from 1 to 8 days. They are advertised in Wind Surfing and other magazines. Two of them are Cort Larned (800-831-SURF) and ABK Sports (415-927-8835). Local shops also sponsor occasional evening clinics on topics such as rigging and safety.
There is nothing like a vacation to Maui or Aruba to improve your skills. Most windsurfing vacations have instructional packages.
Most localities have a local sailboard association. Join the association/club in your area. You will get a newsletter, meet some great people, and help improve the sailing sites in your area.
Surf the web. There are dozens and dozens of windsurfing related sites including a bulletin board (rec.windsurfing).
Sail Hard, Have Fun! 
In 1976 at the North American Championships, sailors had heard that a 13 year old kid from Oahu could sail pretty well. However, this skinny kid blew everyone away in the free style by calmly flipping his board on its side, standing on the rail, and sailing away. The kid was Robby Naish, the place was Berkeley, California. The sport has never been the same since.
Here are some tricks to get started (from easy to difficult):
Sail Clew First. The easiest way to get into this position is to not flip the sail after jibing. A more interesting way is as follows: While sailing on a reach, first move both hands back on the boom. Reach your front hand back across your back hand to the end of the boom. Flip the back of the boom forward and reach over on the other side of the boom. This maneuver will help you learn how to duck jibe.
Sail Downwind Tail First. Come head to wind as if you are tacking. Move in front of the mast and pull the sail perpendicular to the board (in the downwind position). Move out to the bow of the board in the sailing downwind position. The trick is to move far out on the bow of the board so that the skeg is out of the water. This maneuver is great practice that will help you do nonplaning jibes going the other way.
Pirouette. Sail on a beam reach in light wind. Move the sail across the board in front of the mast (the same position as when you started up, step 2). There is a position where the sail will almost balance on itself. After you find that position, let go of the boom, pivot on the balls of your feet (spin around 360 degrees), and quickly grab the boom.
Sail 360deg. Begin as in the pirouette by finding the balance point of the sail, and then do the following: Swing tip of the mast toward the wind. Step forward of the mast on the leeward side of the mast, pushing the clew in front of you. Continue pushing the clew around and follow it until you have circled the mast. You must be quick!
Helitack. Start out as if you are doing a normal tack. When the board is pointing directly into the wind, instead of moving in front of the mast, push the clew forward and through the eye of the wind. In other words, you tack, but you stay behind the mast and the sail goes in front of it.
Head Dip. On a beam reach in strong wind, lean way back with your arms straight. Bend your knees as when you do the limbo and dip your head in the water.
Splits (for the Gals). This trick is one even Robby couldn't do. Stretch out on shore. It helps to have your booms rigged lower than usual. Sail on a beam reach in a light wind and go for it.
Rail Ride (Robby's trick). While sailing along, reach one foot under the edge of the board and pop the board up on its edge, i.e., rail. (I kid you not!). At first you can sail with one foot on the centerboard, the other shin resting on the edge of the board. Then stand up with both feet on the edge of the board (rail).
Not to be outdone, a few years after Robby invented the rail ride, Rhonda Smith performed the splits while sailing on the rail! Ouch!