Something else I look at when I'm polishing a book prior to submission is pacing. If I'm reading along and find myself less than engaged, thinking I should skip over a part or go make a cup of tea, that is a big red flag. It means that part is -- horror of horrors! -- boring. Or to put it another way, too slow.
That is Really Not Good. I have some thinking to do, and then some revising.
Often a boring part comes when I'm trying to get from Point A to Point B in the plot and I haven't figured out the best way. Sometimes I realize I don't have to explain or describe that transition at all. I can say, "Three days later" and just get on with the story.
Sometimes I'm repeating previous information. This can be a tricky call, because let's face it, readers don't always, or even often, read a book in one sitting. Details can be forgotten. So I won't say never repeat anything. I'll just say be careful how many times, and in how much detail.
Sometimes something I've discovered in my research that I find really fascinating can bog down the story. Readers want to hear about the characters more than, say, financial transactions in the Middle Ages. Again, it's a judgment call, but if I find myself wanting to skip ahead, that means I've got too much unnecessary information.
Some people write really fast-paced, non-stop-action books. Some people write a much more leisurely paced story, and others something in between. There's no right or wrong when it comes to overall pacing; that's part of an author's voice.
But whatever your particular pace, you don't want to let the reader to hit a spot where s/he thinks it's time to take a break.