One of the first things Doc said is very important. Always check to see how you story ends up in print, compare the changes. If the editor will let you you may even sit with him as he edits your story. No one is going to expect you to remember all the style changes and things that are corrected right away, but be sure to try. It won't be long before that's natural.
The smaller beats are sometimes where you learn the most. Community colleges, small high schools, losing programs, these are the people that don't expect the coverage, so they are thankful and often more accommodating than those that do expect to be covered. You can learn a lot about how to interview, and what to watch for here.
Be a journalist first. It doesn't matter that you may have just seen the game of your life. What matters is can you convey that to your readers? So many youngsters I have seen get into sports journalism because they love sports, and they think they can write. The passion must be for the art of the writing, not the sport. Because you will get crappy assignments. For every Seahawks vs. Packers NFC Championship games out there, there's 10,000 Buttface High blows out Joe Schmoe Tech. If you can't make a good story from Buttface High, don't expect to see the Hawks.
And don't be driven by the desire to see the Hawks. There are tons of us in Texas that much prefer the prep beat to the Big 12, or the Pros. Yo may find that's you. You may find its not.
As for writing now, keep it simple until you have mastered all the things the boss looks for, then test yourself a bit. Look for a different angle, try a different writing style. In other words, don't be complacent. Some of those attempts may fall flat, but a few will make you proud to be a reporter, and all will make you a better journalist.
And finally, keep having fun. Yes the pay sucks, the hours suck, your social life can suck, but at the end of the day, remember you are writing about sports. And sports are fun.