For a start, Don’t tell them, “I’m not sure what I want, but I’ll know it when I see it.” That doesn’t help anyone. Those words will likely get any talented designer running for the hills or at least politely declining your project. Another golden rule is to refrain from doing the design work for them. A designer doesn’t want to see the layout of your design. Instead, tell them what you want to achieve, the market you aim for, and what mood and emotions you want to inspire. Feel free to share graphics like logos etc., to help guide your graphic designer. Also, while it makes sense to be clear on costs, don’t try and lowball your designer with the promise of more projects to come.  If your project is overly complicated, don’t expect your designer to immediately produce an estimate or quote. A professional graphic designer will want to do some information gathering before they can quote fairly.