I have done a little bit of skateboard shooting and it is a harder gig than it looks. The good thing is they practice a lot so you can practice a lot. Here are a few random comments.
Find an angle. Often the background is dead boring, like in these shots. A chain fence. Other random people. These are things that will distract, but a good angle cuts them out.
This can also
make the session more interactive. You can get a good energy going with the skaters. If you get down on your back you can have them jump over you. Get an angle from underneath! Do tricks together! Skaters naturally love photographers since all their mags are full of cool shots they want to be in.
Pick your depth of field. This is another great way to eliminate annoying background elements and also be creative with bokeh. In these shots you have very deep DOF and it is not needed. Shallower DOF also helps you get your shutter speed up. (Though it seems you had no problem with that.)
Go for motion blur! This sport is dynamic and capturing the motion is what it is all about. Instead of the cloning trick, signify movement with actual (unfaked) motion blur. For this a tripod is useful, especially a deadly small one that won't get in anyone's way. Place it somewhere cool and trigger it via IR. If it's bright you might need some neutral density filters to slow things down.
Go for the drama. Big jumps are wonderful if you can emphasise the scale. Grab a wacky in-air posture. Shoot spills, crashes and mistakes. Capture the expressions in people's faces. Don't forget to shoot spectators too!
Post-process your heart out. There is nothing sacred in this sport; it's all about pushing the image envelope. Get graphic. Get bold. Get wacky.
Here are some examples from a competition I shot. They could really be improved but maybe they demonstrate some of what I am talking about. I was severely limited here by the fact I had to shoot from the audience. I also had a set of batteries fail for no reason and so had to run to a store to get more. (Yes, I had two sets but one was low for no good reason.) This meant I missed some of the contest and lost my position at the fence. Click through for larger versions. Shot with the K100D Super.
Have fun the next time!
Fall (Shot with the FA 77mm Limited.) Broken (Shot with the Sigma 70-300mm.) Jump (Shot with the Sigma 70-300mm.) Spin (Shot with the DA 16-45mm.)