Although objectively I know there are far more authors in need of virtual 'author's assistant' services than there are trained virtual assistants to meet their needs, the first question I hear from someone considering adding to their virtual skills to work with authors is: "How do I know I can find clients if I invest in getting additional training to work with authors?"
Part of the answer is to know where authors and aspiring authors hide: at professional networking groups, at trade associations, such as for HR professionals, accountants and attorneys. Volunteer to give a talk about self-publishing or about doing a virtual book tour. You will find that aspiring authors really want someone who knows what all the steps in the process are and can execute them.
Do a press release whenever you've taken a training class that will show authors you have the skills to serve their needs. Write articles directed at authors giving them tips of the trade. Send out helpful emails to your list suggesting to them if they are thinking of becoming an author you have some great training and other resources for them.
When you do talk to a potential new author client, prepare to do some education. So many authors are open to getting help, but they have no idea what to ask for. Develop a checklist or graphic that shows them all the parts of the publishing process and what services you offer within that. Some virtual assistants specialize in aspects of the publishing process - self-publishing, marketing, manuscript preparation, research or other aspects.
There are so many benefits for an author of working with an author's assistant, but you may be called on to demonstrate those. Refer an author to testimonials from satisfied clients (whether they are your clients or just authors who have used an author's assistant). Refer authors to objective articles on using author's assistants on author sites. Sell the author on the amount of money and time you can save them over doing this work themselves, demonstrate your knowledge of technology and help the author see how much your work will free them to do the work only they can do.
Be prepared to answer questions about costs. Most authors have no idea how to judge the value of these services. It will also be important to have a contract with the author as you might with any other client so that expectations are clear.
Becoming an author's assistant is a very rewarding experience. Once you establish your reputation as a pro in this field, referrals from satisfied clients will become your best marketing tool.