At this stage in our book proposal, we are going to pause and take a brief break. Everything we've done so far are things you might find yourself submitting during a general submissions process. Since every publishing house/agency is a little bit different, some might want your to query with a letter and a summary, some might want a submission with letter, one-page summary, series summary, and first three chapters, and some people just want a simple query letter. Everyone is different, and that is why it is so important to always check the website of the publisher/agency you are submitting to to check for their most recent guidelines.
After this point, everything we will work on in the book proposal will be geared more towards marketing. These elements are rarely submitted during a submissions process, but they are important things for you to consider, especially after your book is under contract. However, don't think you should wait until then to start brainstorming. You never know when someone will ask you about your marketing plans, and these days, authors are expected more and more often to have some sort of idea in place.
But that will be for the second half of this month. For the rest of this week, you should continue to polish your cover letters and one-page summaries. Why? Because in the near future I'm going to run a contest for cover letters/one-page summaries. There will be 2 categories: cover letters only contest for picture books, and cover letter plus one page summary for middle grade and teen books. I know MGs and teens that it's unfair that you have to write two pages, but it's really hard to do a one page summary of a picture book. The winner in each category will get a free critique of their full picture book manuscript or the first 3 chapters of the MG/teen manuscript (depending on which category he/she wins). I don't have a date for the contest, but as soon as I do, I'll let you know.
Until then, keep practicing. And if you haven't tried posting for feedback on the Buried in the Slush Pile forum, you really should. Everyone's been giving great comments over there.