Whether you are trying to capture professionals, kids, or something in between; there are a few key considerations when taking taking sports photographs. Sports offer a lot of variety and opportunity photographically. Not many other settings allow you to capture emotion, action, and great surroundings all at once; and you might get to have a beer and relax while doing it!
Obviously, location is everything. You need to be able to move around and get into position to lower the level of competition. But even if your seats are up in the nosebleeds, you can still get some good images. Including a skyline, stadium, fans, etc... not just the athletes on the field, can yield very good results. Many stadiums also restrict lens size, so if you are not along the sidelines, your shots will be limited anyways. In other words, work with what you've got!
2. Pre-Visualize and anticipate
While you may not be able to see into the future, going in knowing a few images you would like to capture will set you up for when/if they happen. It is a lot like the athletes on the field; they know the situation and what to do depending on what happens. Knowing the sport you are photographing will allow you to anticipate what might occur and if you have a shot in mind you will be ready for when the moment arrives.
3. Use a high ISO speed
This one is a bit technical and not everyone has a camera with the ability to adjust this setting. Shooting at a higher ISO 400+ will allow you to stop the motion much easier than a lower ISO. But what about grains you ask? Yes, you will have a slightly grainier photo, but with the newer cameras this doesn't become an issue until you get around 2400+. Though this is the case for most cameras, it varies so experiment! Using a higher ISO will also allow you to shoot without a flash. This is more of an etiquette and common courtesy thing, though many professional and college level athletics prohibit the use of a flash. I really doubt a batter wants a bright ball of light in their field of view just so that you can get a picture of them.
Now that everyone has a camera these days, your photos are bound to look like everyone else's unless you do something different. Don't be afraid to hold down the shutter and fire off a bunch of shots; you can always delete them later!
This list is by no means comprehensive, but it should give you some tips to make your shots a bit more compelling. There is always a sporting event going on somewhere in your area (it doesn't even have to be an organized event!) As with anything else, practice, practice, practice.