Writing a perfect fiction book proposal was never an easy thing to do for book writers. Not only they just finished the job at a book, a job that may have taken a few years, but they now have to persuade fiction book publishers that what they write is great and it will fast become a best seller. Because if you do it wrong (the fiction book proposal) you will get screwed so fast you'll have to publish by yourself your book or even be forced to throw it.

Let's see what do you have to do to write the best fiction book proposal and what are the main common mistakes in these kind of proposals.

When you are writing a fiction book proposal you should know the following three things: always have a synopsis in the ficiton book proposal; know that a proposal is intended to be a marketing tool; the synopsis must be well written and should be engaging for the reader. 

Already having some experience with fiction book publishers, wrote five myself, I can speak about common mistakes me and other SiFi made when we submitted incomplete a fiction book proposal because we were sure the publisher will read the script. In fact they do read your script. However, if you are not paying attention to the proposal and intentionally forget to include a synopsis or other important details, the publisher (if it is an important one it's more plausible for this to happen) may even reject your book. They won't care that you have an amazing script, if you are thinking that you're better than them they will have to remember that you need them more than they need you. You might be a great writer so don't screw it up by sending junk instead of an at least good fiction book proposal.

I said your synopsis should be engaging. You shold stick with writing the synopsis until you find the best form of it. Think clear and remember that you want to amaze and agent or publisher who probably read tens of scripts each month. Be sure the agen will be interested even after reading the first sentence of your synopsis before you send the fiction book proposal to a SiFi publisher.

One of the biggest mistake I've made the first time when I send a fiction book proposal was to not include the ending in the synopsis. And what a mistake that was. My back-then agent was so frustrated that he told me I can work on a fishing ship better than write. So, add your ending to the synopsis.