hm....
1) NO MARY-SUES/GARY-um....whatever-ues, PERIOD. these are OCs that are perfect. literally they are perfect, flawless, and completely dull. you and i know that people are not perfect. thats what makes this world so interesting
2) let the world be your source of imagination. look up William Wordsworth's "The Tables Turned" for more details.
3) Don't rush and don't pile. Take your time writing if you think carefully or "slowly", and don't add on too much, like me. i made a HUGE boo-boo by writing a prequel and sequel at the same time and although both are actually doing well, its a strain. along with the 6 other stories or so i'm writing.
4) be articulate but not too articulate. don't make your sentences so short the story's choppy but don't elaborate to the point we snore. use vocabulary but don't go overboard
5) be grammatically correct. spelling counts, too. make it easy for us to read and understand.
6) i don't recommend script-writing. its my opinion and my suggestion.
7) be creative. think of a situation, something interesting, then create all the bits and pieces that add up to that one moment. get complex - complex stories are good. then putter around with the consequences of the situation. create short stories, then move onto whatever you feel most comfortable with.
8) you don't have to write within a certain genre or a certain type of story. although sokairis and soraxrikus dominate the known fanfiction domain (well, in fanfiction.net at least; i'm pretty dumb when it comes to forum-run fanfiction threads) you don't have anything to fear if you want to write a more various range of crack-couplings.
9)remember to watch out for the contents of your story. i never thought of it before but a lot goes into the details of a story, including certain elements that society feels is not appropriate for kids under the age of 13. language is quickly corrected on this site, thank goodness for the quick fix, but just be careful how to use it. i prefer the more casual way, which equals a lot of short, incomplete sentences and questions, but it depends on how comfortable you are with writing
10)...and above all. have fun.
if you have any more questions, feel free to ask around. i'm sure there are waaay smarter ppl out there who can help you, no?