Well, I'm not sure how experienced you are, so I will proceed to give you general tips.
Read up on works by famous writers and decide which style (Neoclassical, Romantic, Naturalistic, Realistic, etc.) is best for you (you'll have to practice writing to find out which style you like most; don't be afraid to make mistakes, because that's how you learn). Decide what type of writing you want to work on: fiction, non-fiction, prose, poetry, satire, novel, narrative essay, etc. etc.
Along with reading books, practicing, and finding out which style of writing suits you best, learn the basic elements of any good story. Knowing the definitions of climax, rising action, falling action, protagonist, etc. and the place of each in a story will help you in the long run.
Decide on a plot and the main characters involved. Make sure that the characters have depth and personality (unless you're using the Neoclassical style, but that's a different story). Keep the story on-track: work on a main theme. You can have sub-plots and themes too (and they should ALL reasonably tie into the story), but focus on the main point the most.
Also remember that language is your friend, not your enemy. Use language to emphasize your point; be either concise or flowery (concise = Realist; flowery = Shakespeare). Practice using similies, analogies, puns and personification. All of them will add to the story and help the reader understand the plot and/or characters more clearly.
Finally, once you have written something, check it over and make sure that there are no plotholes. If there are, work around them and/or answer them; but don't be too explicit if you
do answer them. Good writing usually demands subtlety.
I hope that helped. Remember: practice, practice, practice. Don't give up if you don't get it right away, because writing takes work, but it can produce brilliant results if you get it right.
