Keep in mind that some contracts can affect your writing life far beyond the confines of just the work which is officially the subject of the contract. The main dangers to watch out for are inappropriate option, non-compete and revised edition clauses, and assignments of copyright.
Some authors agree multi-work deals, with advances relating to each work included, and that’s generally a good thing – so long as first-time authors, especially, can cope with the pressure of writing books two and three under the pressure of expectations and deadlines.
However, rather than committing both parties to further books, some contracts simply demand that the author give the publisher a 'right of first refusal' on their next related work, meaning that publisher must be given the option of accepting or refusing the work for publication before the author can take it elsewhere.
If you're happy with your publisher you might want to submit your next work to them regardless; a publisher compelling you to do so against your will is another matter. Contrary to popular myth, option clauses are as legally binding as any other commitments in a publishing agreement.
Fiction writers lucky enough to secure film or TV deals can find themselves unable to control spin-offs from the adaptation of their original book. Non-fiction authors, in particular, need to be very wary of clauses which restrict them from writing other works on the same topic – generally described as ‘non-compete’ clauses.
On top of this, watch out for contracts which give the publisher, rather than the author, the right to produce revised editions of an existing work, without necessarily even involving the original writer. This situation can arise via the wording of a revised edition clause or simply as a side-effect of the author assigning copyright.
These restrictions may or may not be reasonable, depending on the individual situation. If you are updating the 17th edition of a long-established work you are likely to have much less say over revised editions than if, for example, you created the first edition of a seminal work of reference.
A non-compete clause is much less onerous if it has a clear definition of what constitutes a competing work, and if the restriction lapses after a given time or when certain conditions are met (such as if the author’s royalty income from that work falls below a stated level).
As always, we urge you to bring all contracts you're unsure about to us for checking. The devil is in the details and our highly-trained advisors are always happy to break them down for you.