Don't just write what you know. Do write what you want to read. But if you write what you don't know, do research it because people who know it won't appreciate wrong facts.
Don't just write when you're inspired and excited, because that will lead to hundreds of Chapter Ones and few Chapter Twos. However, if after the first inspiration, you don't ever get excited, do evaluate the story. There could be something wrong with it.
Don't just learn to write by reading "how to write" books. Do read real books. Writing how-to has its place, but stories get writing how-to into the subconscious in a way nothing else can. It's more fun anyway.
Don't worry about spelling and grammar and style and little nitpicky details in the first draft. Just get the story down. But do fix those things later. That's what second, third, fourth, fifth, sixth, and seventh drafts are for. (That's about how many it took me to get The Experiment right.)
Don't be afraid to let people read your story. Stories are meant to be shared. But do remember you can't please everyone. Write the story you want to write.
Don't freak out when you get writer's block. Go do something else. I usually ride my bike when I get stuck, and it really helps. (My mom heard about a study that shows exercise helps break writer's block and get creativity going, which I thought was really cool.)
Don't be afraid to rewrite your stories. Only a genius could get everything right on the first try. Do take some breaks between drafts, though. It helps to get a fresh perspective.
Don't try to conform to someone else's writing style or method. Everyone is different. Do find what works for you. But don't be afraid to change your method. As people grow, they change. I know I have, and my writing method has changed.
Don't forget to have fun. What's writing for if you can't have fun with it?