One of the key steps that you can do with the creating of any book is to create and review proofs. One of the proofs that I like the most is created when you have pretty much finished the manuscript. The book has gone through the first round of editing and you are now doing the first pass at the design and formatting. At this stage I like to create a pdf and have it printed out and bound, usually with a spiral binding. This gives you your first real feel for your book. You can hold it and open it and can really visualize it. This is also a great place to do a second round of editing. The difference is that instead of doing it on the computer screen you are doing it with a real book. You will see things here that you just don't notice on the screen or even in just pages. All kinds of stuff shows up that was missed. I feel that you get a much better book doing this print proof. I highly recommend do it.
It is easy to do. Create a pdf of the interior and of your rough cover. Take the files to Staples or Office Max and print them out. Crop them and have them bound with plastic covers. It doesn't cost much and you will be surprised at what you see.