Well...generally a contract is written up that both the publisher and the writer agree to. While some parts are assuredly standard...I would imagine that you or your agent can also work out some areas particular to YOUR specific contract. A contract may state that YOU agree to doing more work, rewrites on a single book, or could include that you will have the second..third...book finished and ready for first review by a particular date. It may lock you into agreeing to be present at "X-number" of Book Signings....and spell out what part you may play in promoting the book as it would what part the publishing house will play. The contract will assuredly spell out the payment total, and if there are installments...what they will be and when you would receive them...additionally, it would cover any royalties you would receive. In some cases it may state that you have the right to refuse...rewriting what you've been asked to fine tune, but quite likely this is a double edged "right" because it would include that the Publisher has the right to DROP YOUR BOOK...if you do not do the rewriting! Always keep in mind...a Publisher doesn't make suggestions or even demands without a pretty good reason. They do not make money EITHER if your book does not sell...they are motivated to see your book become a success...then you tend to get a bit more favor and flexibility with things.... once you ARE a successful Author!