It's only natural that after spending months or years writing a book you would want to get it published ASAP. But waiting a few weeks could actually be better.
The plot is perfect, the characters are colorful, and you've just typed, "The End." Congratulations! You have a finished novel! But don't get too excited just yet. Like any other excited author, you're raring to get your manuscript to print as soon as possible, but sitting on your book can serve some very important functions.
When you work intently on a project, your focus to narrow into your topic and you subconsciously block out extraneous influences. While this can be good for your concentration, it can be bad for your creative flow. In fact, most of what people refer to as writer's block is exactly this. Once you've finished your book, put it away for a few days. Even a few weeks or a month will be fine. This will give your brain a chance to get out of the tunnel it's been thinking through and expand to consider other possibilities.
After you've set it aside for a while, go back and read your book. After even a few weeks your book may look very different to you. You might even find that you've forgotten about parts that you've written, and are able to see it with a fresh set of eyes. This is very important for editing - not just for typos and grammar but for plot and character inconsistencies.
Make a list of things you find in your novel that you need to address. What do you need to add? What do you need to take out? What doesn't make sense to you? Is one of your characters acting out of, er, character? Is there a hiccup in your plot? How can you make the most important scenes more intriguing to the reader? How can you add more drama, more action, or more emotion?
Go through the book, taking one item at a time, and repair it. Then read it again. Do this until you're happy with your finished product. Putting aside a book you've just written can be quite a challenge! It's natural to want to move forward with it as soon as possible, but by giving it the attention it needs, you will be able to create an even more spectacular story.