Yes, say the experts, there are mistakes people make over and over when working with an accountant. Talk to yours about what those mistakes are and how you can avoid them. Some of the most common include not being completely honest and up-front about business or personal finances and goals. Your accountant can offer more than mere tax return services if you share information about your business, your life, your dreams and your financial problems.
Hand-in-hand with this is the mistake of not taking your accountant's advice. Not that you should blindly follow whatever is said, but consider the advice and explore the subject further with your accountant if you have questions or disagree with it. You're consulting a person you consider an expert. Discounting that advice for no good reason goes against the very reason you hired an accountant in the first place.