1. Try to insert spaces between each set of five or four paragraphs in your writing. No one likes to read a big wall of writing...
2. Add little hints of humor. Your stories don't have to be filled with comedy, but little humorous lines here and there keep people interested. A laugh is a powerful thing.
3. Try not to create stereotypes out of characters. Make them interesting. No one fits into a stereotypical label (atleast not unintentionally). Make them human-like. Different.
4. No "completely good" or "completely evil" characters. Yin and yang. No one is completely yin or yang. That should be reflected in your characters.
5. Oh, Lord, NO NET-SPEAK. CHECK GRAMMAR. CHECK SPELLING. Have I said enough?
I hope that this advice is helpful to any budding authors. Even if some of it has already been mentioned in other advice topics, well, some things just can't be mentioned enough.