Shooting action sports can be overwhelming and strenuous if you lack the proper knowledge before going out to shoot. Whether you want to shoot motocross, mountain biking, snowboarding, ect.... for the most part all of the same rules apply. Once you start to master these rules your portfolio will benefit from it. Since I get a lot of questions about my action shots I though I would break it down for you guys.
The best way to get better shots is to shoot professional athletes. I'm not saying you need a red bull athlete, local pro or intermediate athletes will get you the shots you want. Just approach them, most of the time they are very friendly towards photographers since you can help get them get exposure, and in turn your building a better portfolio. Worst case is they say no and you look for a different athlete. I think it is vital to shoot the best possible athletes that you have access to. It's like shooting celebrities, even if you don't have the most dynamic shot people will still recognize them and want to know who took that photograph. Just start going to the local ride spot, track, ect... start shooting and make friends. Then they will start inviting you when they go out.
When you are out shooting communicate with the athletes, see what lines they are hitting, what berms they want to blow up, and what jumps they feel good on. If you just show up and start shooting without any clue to how the athletes are feeling about certain areas you're basically running around like a chicken with it's head cut off. It can be a compromise, sometimes what the athlete is feeling won't make for the best composition, or the light might not be what you want. But I have usually found that when you shoot what the athlete is comfortable on they give you the show you came for. Don't be afraid to ask the athlete to try something tho. They are usually down to do whatever it takes to get a good shot.
I have found that when composing your shot that you can go about it two ways. Shoot close with a wide angle, or tight with a telephoto. If I was shooting somewhere with a epic backdrop then I would shoot with a wide angle to include the landscape. When I am shooting at the track I usually shoot with a telephoto. I see a lot of beginner photogs shooting wide at f8 or higher, so the subect is far in the frame, everything is super sharp, the background is boring, so in turn the image lacks interest. Try to keep in mind that you want the viewer to see what the athlete is doing. Try to include the take off and/or landing. Try to be very conscientious of your composition. Try not to have distractions in the background and not to cut off the subject in the horizon line . Make sure the the photographs flows.
With wide angle lenses don't be afraid to get as close as you can to your subject, it can make for a really killer shot. If the subject is going to be closer than 4 feet and moving faster than 15mph i recommend pre-fousing instead of tracking, unless you have a 1dx.
Keep in mind that color can play a huge role in making your athlete pop from the background. I like to keep my color pallets pretty simple and try to keep the number of different colors to a minimum.
When I use stobes I am very particular on how they fill the scene and light the subject. It can be very easy to not have enough ambient light or poorly places strobes. I usually back light the subject with one strobe and for the front strobe I will have it about 45 degrees from the camera. Remember when back lighting the power does not need to be as powerful as your key light,you want detail in your highlights. I use two 5080ex's on tt5's when I do strobe, thanks to Lear Miller. If you can find someone that is willing to hold a couple reflectors I recommend doing so. You would be surprised how much light you can bounce off a couple 4x6 reflectors, plus its a lot cheaper than strobes and in mid day more effective.
Get creative. Photography is a relentless industry with every photographer trying to be the next big thing. Try new angles, light set ups, ect... The more you try new thing the more likely you will develop your own style. Ask the athletes what they think would be a cool shot.
Being that it is such a competitive industry any advantage you have will only put you that much more ahead. Photoshop is such a powerful tool and in my opinion a necessity to get the most out of your image. I usually spend quite a bit of time on an image to make sure it is exactly how I envisioned it. I tend to underexpose my shots by about a half stop. I do this because once in photoshop I will open the image, make my adjustments in raw, open the image, then re-open it in raw add about a full stop on the exposure slider and open it. Then I will take the two images and blend them together using layer masks. For post work I do a lot of dodging and burning and selective color adjustments. I also open a B&W layer and turn it to soft light. Use layers mask to fine tune your layer adjustments and really get the most out of your image.
Don't be afraid to shoot at high ISO's. With the noise reduction software available you shouldn't hesitate to crank that camera up to 6,400 iso.
Both the images below were shot at 6,400 iso.
I own both a Canon 7D and 5Dc, and I honestly tend to lean towards the 5Dc. The reason being is that I don't really need the frame rate and focusing on the 7D since I tend to pre-focus and wait till the subject enters the shot and pray. To me full frame just has so mush more to offer. But that doesn't mean I don't need the 7D for some occasions. My only point is don't get hung up on what camera and lens you have. None of my shots have been shot on L glass. I use a tamron 17-50, 85mm f1.8, and a kit telephoto lens that i think is a 70-250mm. Don't let your discouragement jeopardize you from going out and shooting.
Most importantly have fun and make friends. I hope you were able to learn something and if you have any questions on something I didn't cover or a specific set up for a shot feel free to ask.