This post isn't about marketing or selling books per se, but it does touch upon a subject that can definitely affect your success as a professional author and that is acting and operating as a professional author. But, what does it mean to be a "professional author?"
You have published a book, it is being distributed, you have done book signing events and you are earning money (even if it is a small royalty) each time a copy of your book is sold. By any definition in the publishing world, that makes you a professional author.
Publishing (writing, editing, designing, marketing) is a business, just like any other business...banking, teaching, construction, selling insurance, etc. Whether most people like to admit it, being an author is basically a job, an artistic one, but a job nonetheless, and people who work a job are expected to act with a certain amount of professionalism. Some authors have made the comment to me that "I have never written a book before. I am new to this." While that may be true, everyone has worked a job at some point in their life, and so they should have a pretty good idea of what is expected in a professional working relationship. It is no different in publishing than it is in any other industry.
Should not only show up for their book signing events, but be on time (early would be better). You don't want to be known amongst the bookstores as the author who can't be depended upon to be an event that they have set up and worked to pre-promote. If there are special circumstances (illness, death in the family) call the bookstore and explain the situation to the manager. They are people, too. They will understand and they will likely postpone the event.
Should be gracious with bookstores that are hosting their events. Bookstores are under no obligation to schedule a book signing event with anyone. The fact that they have agreed to let you come to their store and let you promote your book shows that they are already supporting you. Yet, some authors get angry with bookstore managers who "didn't take out an ad in the paper" or "promote my event." I have even heard of authors who have berated managers in the store and leave because there was no table and chair set up for them as soon as they walked into the store for their event. Would these authors behave the same way if they went to a scheduled meeting for their day job and the people they were meeting weren't ready for them yet? Probably not.
Should not have unreasonable expectations of their friends and family. Writing a book is your dream, not theirs. Don't expect that they will be as excited about your book coming out as you are. It's even possible that they won't buy a copy of your book (in fact, they will probably expect a FREE book). I already know that my parents aren't going to buy my book when it's finally finished, because they aren't really going to be interested in a book about how to sell books. But, they'll still want a copy that they can show to their friends. That's OK. They'll each get one as a gift.
Should read EVERYTHING that their publisher sends to them. This includes the publishing contract. You would be surprised at how many authors don't read theirs thoroughly, or ask questions if they don't understand something in the contract. At my company, we provide a marketing guide for authors before their book goes to print. I can always tell when an author hasn't read theirs, and it happens a lot. Your publisher, no matter who it is, provides information to you with good reason. You wouldn't ignore paperwork that crosses your desk at work. It's the same with forms, guides and contracts sent to you by your publisher.
Should deal with their publisher's employees in a professional manner. There is no doubt about it, a book is an author's baby. You have poured your heart and soul into producing it, and it is an emotional experience. However, publishing is still a business. If there is an issue you need to discuss, it is definitely acceptable to speak with your publisher about it in a professional manner. Calling the publisher and yelling at the employees or writing emails in all caps with four-letter words sprinkled throughout is not acceptable, just as it would not be acceptable at an author's regular day job. It's rare, but it does happen. When communicating with your publisher, stop a moment and think to yourself "would I say or write this to my co-workers or supervisors?" If the answer is "no," then it definitely should not be sent to your publisher, no matter how upset you might be.
Should have reasonable expectations. There are no guarantees in life, and publishing is no different. If someone starts a new restaurant, salon, construction company or any other kind of business, there is no guarantee that it is going to succeed and make the business owner a millionaire. Writing a book is no different. Hard work and persistence can and do pay off in the publishing industry, but the overnight successes are rare. Bestselling authors are nearly as rare as Grammy Award-winning musicians. Plenty work in the industry with moderate success, but not everyone reaches that level. It's OK to shoot for the stars, but realize that no publisher or publicist can guarantee success.
Remember, nobody achieves success on their own. Those who are truly successful, whether it's Donald Trump, Bill Gates or James Patterson, needed somebody's help at some point in their professional lives. For an author, those people are the publisher, the bookstore managers, the publicists and many people they may not ever meet face-to-face along the way. Treat each one the way you would like to be treated, and you may be surprised at the results.