You don't need to have ever played the game you're photographing, but you do need to have some idea of how it works. If you're a complete newbie, go online to familiarise yourself with how it's played. Pretend that you're going to play it yourself. What's the objective, and where do players need to be to score the point?
Flashes distract athletes and are generally bad form at sporting events. That means you're going to have to work with the light already there, and that means bringing fast lenses.If your focusing is spot-on, you should be able to get away with it.
When shooting players, remember that humans are always looking to connect with each other using our faces. Action shots should always feature a facial expression, whether that expression is one of joy, concentration, frustration, or just intensity. This is how photographers capture the emotion of the game, and it shouldn't be underestimated. It's easy to capture a photo of the player running down the field, but capturing an action shot with the sweat dripping off of them as they intensely concentrate at the task at hand is another thing entirely.
What you don't want to compromise in your sports images is your shutter speed. Slow shutter speeds are not only going to lead to camera shake but also to motion blur. Sure, in some limited circumstances and with some planning motion blur can give the composition a fantastic artistic look. But that doesn't come around by accident; it's tricky to pull off. Most of the time, you want to avoid motion blur like the plague.
While you're capturing the story, you might find that wide-angle shots can capture the scope of the events better. Not every sports shot is zoomed and cropped to the max. If you decide to go this route, you really should have a second camera body set up with your wide-angle lens ready. You can't waste time switching lenses , and you probably don't want to risk it anyway. Keep your equipment safe and clean by setting everything up in advance. If you're carrying two cameras, consider investing in some comfortable shoulder straps or even a holster style carrier.