- Passive voice: It slows action down and you want action in your book. In case you’re unfamiliar, passive voice is using any version of the verb “to be” including are, am, being, was, is, be, become, etc. Sometimes it is the only real option, but that’s the case less than 25% of the time. It’s boring and, well, passive. Even when it doesn’t feel like you’re adding action– changing “is” to “seems” for example – still unconsciously registers with readers as less passive. It’s actually a good exercise for you to go through and see how many passive verbs you have used as it will make you think more carefully about word choice.
- Flat characters: Think of Sex and the City. Miranda, Samantha, and Charlotte all have very distinctive and easy to pin down personalities whereas Carrie does not. She’s a writer and likes fashion, but neither of those are personality traits as much as one is what she does and the other is what she likes. But it’s very easy to say that Miranda is driven and judgmental and passionate, and Samantha is sexy and independent and impulsive, and Charlotte is traditional and caring and open. Ancillary characters are easier to give more personality because, as they are not the main character, they are easier to see from a distance. But you need to have that distance to see your main character and give her more oomph. This is a common issue when the main character is a stand-in for the author. While Sex in the City proves this can work, the success of Sex in the City is more despite Carrie’s lack of character than due to it.
- Author proxy. When the main character is an author-proxy, it's nearly impossible to see her clearly like an outsider would, and because you (of course) know your own personality traits inside and out, it's not always obvious to you when those aren't expressed clearly. Characters that are closer to "types" are much easier for readers to understand and see clearly right away, and while you might think that "types" are the last thing that you want, in the course of your story you will show us that they're three dimensional. So we start with a well-defined outline and then it's shaded in. But with a fuzzily defined main character, she stays fuzzy. She's never been well-defined and so adding shades of grey to her as we go along doesn't make her character become more distinct. It’s best if a main-character isn’t a lightly veiled version of you.
This information is from Carin's presentation to my CPCC class on Writing Fiction.