I really enjoy reading well-conceived dialogue; it's often the most action-packed part of a narrative, whether fiction or non-fiction. From the perspective of a copy editor, however, it's also the part that requires the most meticulous focus. So, when there's a dialogue-heavy narrative, it takes this copy editor significantly longer to get through it. Why? Well, there are some common pitfalls that many authors have a hard time with.
First, illustrating the manner in which a character speaks causes some difficulty. Many authors think that whatever sentence precedes a quote must end in a comma before the quotation. This is not the case. Take the following sentence as an example:
Jessica smiled. "I love science fiction."
Many authors would place a comma, instead of a period, after "smiled." But is smiling a way of speaking? It is most definitely not. You can smile when you speak, so you could smile and say, "Hi!" You can smile before you begin to talk, too, and imply that you continue smiling after your spoken line. You absolutely do not smile dialogue, though.
Another common pitfall is falling into a placement pattern. An author will become comfortable with always placing the "he said" before the dialogue, or after it, or even in the middle. Authors have the tendency to choose one of the three and stick with it, which ends up feeling kind of stale to a reader.
That repetition carries over to the verbs themselves, too; an author will get stuck on one way of describing the manner of speaking. For example, I can accept that giggling can be a speech action, as in: "You're so cute," she giggled. However, when every line of dialogue becomes "giggled," the verb starts to lose its meaning. This is one of the ways in which a thesaurus can be a valuable writing tool.
Keep sending me dialogue, though - I love it. Just don't be offended when I tear it apart!