At the agent blog of Dystel & Goderich, I came across this wonderful link - 10 Questions Editors Ask Themselves When Evaluating a Manuscript.
Aside from the misspellings (*giggle*), some wonderful questions are asked, about pacing and characterization, about theme and readership. Questions every author who's trying to get published should be asking about every book he/she writes. Some of them seem too simple (common sense questions that should be obvious to any writer), but I think each question is worth carefully considering.
I found myself stopping and thinking about each question as it related to my own novel (Book 2). I could answer "yes" to many of them, but when I had to pause and consider my answer for too long, it made me wonder if there's something else I could be doing to strengthen the plot/characters.