1. Crazy dialogue attribution
Ex. "Whatever," Tom growled harshly.
2. Lofty discriptions
I don't really know how to put it in words, but descriptions in (for example) The Ranger's Apprentice series often seem cheesy and like the author is trying too hard. My first try at my current W.I.P. had lots of these.
Ex. "As soon as the King of Ivor, whose name was Devonian, finished saying this, he took the King of Kavimeras with him into the Benbran forest, which broke off right before the castle walls. As he left, he cued several cooks whom outlaid many types of food on a table several yards to Fredric’s left. The table this food was set on was massive and made of cherry, the surface must have been shined, for even when a cloud blocked out the bright sun, the wood still glinted zealously. The food itself was even better looking than the table, and the aroma with it followed suit. There was hot roasted bread, pies of all varieties, and tasty mutton dripping in juices and butter. There was also a boar, tusks sharp as an arrowhead, right beside many other foods such as stag and puddings. Light wine was placed at every seat of the table and there were barrels of more surrounding them. This food was all imported from the southern country of Fabien for a hefty price of four hundred Ivorian coins."
3. Perfect tenses
In other words, overuse of past and present perfect tenses.
4. Overly-realistic dialogue
Transcribing a conversation with your four-year-old for use in a story isn't a great idea.
5. 3rd Person Narrative POV
Writing in 3rd Person Narrative POV is possibly the easiest way to tell rather than show.