When you are asked to sign a contract, be sure to read it very carefully. Most clients want to simply ensure they are protected, but some contract terminology may leave you in the lurch if there are disagreements about the work completed or other factors.
Be sure you have communicated clearly with the client before you get to the contract signing part, so that you both know what this agreement will entail. Clearly state your terms of payment, the turnaround time you will provide and how the rights will be assigned once work is completed.
When you are ghostwriting, you give up the copyrights to a piece, typically once payment is received. Make sure both you and the client understand exactly when the rights ownership will be transferred.
It is a good idea to consider all of these components before you begin accepting clients, so you will be prepared with your own terms and already know what you are willing to agree to.
Contracts are not a bad thing and should not dissuade you from taking on a particular client, but you do need to take responsibility for thoroughly reading a contract to be sure you can fulfill the requirements.