So you need to communicate something in a visual way but aren't exactly sure how to do it. I understand, you didn't go to art school and the last time you had to open a Photoshop, it was your after school job. Don't worry about it, dude: there are professionals who can help you. We're called graphic designers and we're here to make your ideas a reality.
Know What You Want
Before you sit down with your designer, you should have a clear idea of what you need from them. Consider the final output. It's the graphic designer's job to bring questions to the table and help you refine your idea, but the more coherent your initial meeting is, the better the final work will be. With that in mind, be specific with your feedback. Asking for something to "pop" or "make it more premium" splits my head but above all, "I'll know it when I see it" melts my brain.
Familiarize yourself with fonts, colors and layout to help guide your graphic designer in the right direction. Here's a helpful infographic on '10 Tips for Designing Effective Visual Communication'.
Don't be afraid to draw, whether it's a quick sketch on a pad or a white board, graphic designers are visual people. Chances are good that we will understand you better with pictures, however fast and rough they might be. When searching for inspiration, you can also take full advantage of keyword searches on sites like Pinterest and Behance. They're an excellent resource that you should feel free to share with your designer. If you're feeling exceptionally adventurous, give Canva a whirl. It's a pretty great tool if the only Adobe program you're familiar with is Reader.
There is no one designer that's an expert in everything. More often than not, though we may have an interest in many fields, most graphic designers have one or two areas in which they're extremely specialized. Do you know if your graphic designer works mainly in print or digital? You wouldn't expect a soccer player to throw a touch down pass, so don't expect a commercial print designer to create motion graphics for your video.
Give Us Time
Rome wasn't built in a day, and neither will your website. Understand that whatever we're creating for you, it takes time.
My dream is to one day meet a client who has all of their text and photos readily available on a file-sharing site such as Google Drive or Dropbox. Whenever I update work, I can just shoot a message over and let the client know that there's an updated PDF waiting for them. At that point, they can just mark-up the PDF and re-share it. I find that it's the most efficient way for me to work, but every designer is different—don't be afraid to ask their preferred method of communication.
Every graphic designer is different; each of us is a beautiful, unique snowflake and I'm sure some of them won't agree with my advice. But I've spent a lot of time in cramped, sweaty rooms with my colleagues trying to finish a project before a deadline so trust me, I know our kind pretty well. Now go out there and find a graphic designer!