1) Balance exposition with narrative
Remember: you are telling a story. Start off with scene, or an interesting hook, or a funny character, and tell a tale. You are not writing a Wikipedia entry or a daily news story.
2) Demonstrate, don't state
Same as show, don't tell.
3) Avoid clichés
Simple mistakes that most writers (me included) still encounter. Avoid phrases like "modern society" (generalisation — be more specific), "breathtaking views" (overused — describe the view instead) and "stark contrast" (redundant — shouldn't all contrasts, to some extent, be stark?).
4) Have a strong angle
Ask yourself two questions: (1) What is my story actually about? (2) Why would other people want to read it?
5) Use your full arsenal
You've learned about character, dialogue, scene, description, humour, structure and research. Use them all.
6) Answer questions
If your piece has an interesting question at its heart (eg. Why are fewer Australians having children in their 20s?) you are obliged to answer it somehow.
7) Interview people
Writers don't have much authority over a subject, unless the story is 100% about themselves. Whose authority can you borrow for the story?
8) Watch tone
Be consistent and appropriate for your audience. Cleo is not likely to publish a story with words like "aforementioned" and "thus".
9) Be brave
Take risks with writing. Be imaginative. Editors are happier to see writers take risks that fail, than expressionless, flat writing.