Laundry list descriptions
Readers like to use their imaginations, so try not to go on about how a character looks. It’s better to describe a character based on behavior, personality, and body language.
Spelling errors
No, not “typos”, but mistakes such as changing the spelling of a name several times throughout a manuscript.
Not editing
Yes, those types of spelling errors. Grammatical errors, plot holes, the like. Check out the piece on Dramatic Structure to help with plot.
Wordiness
Don’t use ten words when you only need five.
Having characters with similar names
This confuses readers and makes them work to keep your story straight. Readers do like challenges, but not this kind. This isn’t a hard rule as many successful writers have done it, but keep in mind that they went through vigorous character building. Check out the How-To series for tips on character building.
Research
Readers are all for imaginations, but when it comes to things like typical procedures–police, firemen, doctors, etc, you want to make sure your stuff is right.
Dialogue Issues
This could be tags, punctuation, small talk, voice. Check out my other posts: What We Don’t Say and What We Do Say
Sensory Information
Or lack of. Include all the senses. If you’re writing sci-fi, include more if your characters have them. Check out the Setting post for ways your setting can help invoke your character’s emotions.
Cliches
They are so last summer.
Adjective Overkill
Readers get wary when they read a laundry list of adjectives.
Tenses
Pick a tense and stick to it, only altering for things such as flashbacks, memories, dreams, visions.
Telling
There is a place for it, but for the most part you should aim for showing.
K. L. Reeder 