SHORT DISCLAIMER: these common mistakes are in a completely random order. Some are more silly, some are more serious. :P

1. Deleting pieces of writing because of insecurity. DON'T DO IT! You'll never know when you'll want to pick it up again to revise or to find out what kind of stories you used to write.

2. Showing off. You don't have to add an unending number of adjectives that make you sound smart just because you can. Most of the time: less is more.

3. Naming modern bands, movies, prices in stores etc. This will make your story seem old in no time. Let's be honest: even though you love that particular band now, as time goes by no one will probably have heard of them.

4. Letting your character grin and speak at the same time. ("That's John," he grinned.)Grinning while you speak makes your face look creepy, believe me. It should be like this: "That's John." He grinned. See? Problem solved: first he talked, then he grinned.

5. Letting your conflicts be resolved by some kind of coincidence. This isn't exciting to read at all. The solution to all the conflicts should be planned by you as the writer, yet the reader shouldn't be able to figure it out until the very last moment.

6. Clichés.

7. Using passive language. Example: The apples had been cut. Readers prefer: She had cut the apples.

8. Writing something you think your are supposed to write, instead of something that you would love to write. When your heart just isn't in it, you can always tell!