There are no legal technicalities involved in becoming a ghostwriter. You simply hang out your shingle. As a ghostwriter, you are basically a surrogate writer for someone—often an expert or celebrity—who does not have the time or talent to do the writing themselves. They (or often their publisher) will hire you to do the actual writing. They have total control over the content and you simply write what they want the way they want it written. Depending on the type of book, you often must write it from their point of view—or as if they were telling the story themselves. In ghostwriting you will not have your name on the book and may or may not be given credit inside for “editorial contributions.”
Once you have agreed to accept a ghostwriting job, you may need to have a contract between you and the subject, that lays out how and when you will be paid. Such a contract may not be necessary for articles, especially for customers you have worked with before, as long as they have agreed to your estimate or quote for payment. When the job is completed, along with the finished manuscript, give them an invoice for the work done, based on your agreement.
However, with a book project, you will need a contract with the source person or their publisher. If a publisher is involved from the beginning, it may be a good idea to meet with both the source and the publisher before starting to be sure you are all in agreement as to what kind of book you are to produce and how/when you will be paid. Ghostwriters are generally paid a flat fee—rather than a percentage of the royalties as you might get with a co-authoring contract. When the publisher is paying, your fee may be all or part of the advance. If the source is paying you, be sure the contract indicates that you will be paid whether or not the book actually sells. Generally, the amount you will be paid is based on your experience, credentials, and the length/difficulty of the project. Know what it will take to make this a viable project for you before entering into the negotiation process. If the source/publisher cannot or will not meet that amount, and attempts at negotiating fail, then be prepared to turn down the offer.
If you agree on payment, you will also need to determine when you will be paid. Often you will get half the payment before you begin, and the second half on completion of the project. If it’s a rush project and you won’t be able to work on other paying projects at the same time, you could ask for a greater percentage up front to support you during the work.
The contract or negotiations should also indicate whether or not you will have an expense account. If you will need to fly to meet with the source one or more times (which also involves housing and meals), there will be long-distance calls involved, postage to mail drafts back and forth, and the like, you will want to be sure someone else is paying those expenses.