Kyle T. Webster recently posted an article on this same topic. This is a follow-up to said article, where I add my own 2¢ to it. His main point was that art directors today are increasingly missing the mark where it comes to briefing and communicating throughout projects. Specifically, they give vague briefs when first getting in touch, are not specific about details that end up needing to be specific, and they don't write back if the project gets killed before starting.
I think his third point, about writing back, struck a nerve for me. Call me needy, but I expect a response from people whose projects I have quoted on. I also expect acknowledgement when I send through deliverables. Very recently, I was contacted by a firm about my availability to do a couple editorial illustrations for a new magazine. A week went by since our initial exchange, so I followed up to see where we were at — only to be told their client went with another illustrator. I'm not so disappointed at not getting the job as I am that I had to pursue the art director in order to learn about it.
Prior to that, I had another job on the go with an agency. We were at the second round of concept sketches (often a sign of poor initial communication, or inexperience at working with illustrators), and almost a week had gone by after sending the sketches through. I was the one who had to follow up, and only by so doing did I find out that their client did not like any of the sketches and wanted to kill the project. (As a side-note, I was thankful that I included my kill fee in the original quote — never start a job without a clearly articulated kill fee!)
As a freelance illustrator, I am used to the need to be flexible and turn things out in a hurry. At the same time, I need to have a sense of what's on my plate in the coming weeks. I mentally clear up space for prospective jobs until I am certain they won't happen. So getting some kind of status update from an art director if a project falls through is only common courtesy.
On the point of writing back, it helps knowing that my emails go through when I send sketches or finished artwork. Surprisingly, I often have to just assume my emails went through based on the fact that nobody came looking for them after they were due. But is it too much to ask for art directors or clients to say "Got it, thanks."? I know everyone's busy all the time, but small kindnesses like these really grease the wheels and help boost morale in a given project.
Per Webster's first two points, it is true that many clients give vague briefs or query emails when asking my availability. For these I have less of a problem. If anything, they are good indicators of what the client will be like to work with. It also gives me a chance to demonstrate my experience by asking them the questions they were supposed to ask themselves. Or, put in a less self-centred way, it gives me an opportunity to help a potential client think through their own project. I'm used to doing this with my design clients anyway, who often need a designer to help them understand their actual need or goals for communication. I would say to any illustrator that it's usually unsafe to assume. If a client asks you simply to illustrate a car (as in Webster's example), you need to ask them some questions, like what kind of car, should it be new or old, etc. If the client or AD insists that they want you to "do your thing", that they "trust you" to come up with something great, ask some other questions that will help you understand how the illustration will be used. (Even ask that — how the illustration will be used.) I always ask my clients what the context is and who the audience is. It always helps me find the right angle to approach an illustration from when other details may be missing.
Other than that, here are a few other pointers for clients or AD's working with illustrators:
When contacting an illustrator about work, take some time to review their portfolio or web site to ensure they have a style that suits the project you have in mind.
When you like what you see, please say it! At the end of a project, most illustrators really want to know what you think, especially if you think well of it.
If you are an AD and have feedback, don't hide behind the Creative Director or client and give feedback as though it came strictly from them. Just say what you think, or give the feedback straight-up. It's you with whom the illustrator has a relationship, so it's you they're going to be most willing to accept feedback from. Comments from unknown colleagues or ghost clients tend to annoy more for some reason.
Of course, this list is not exhaustive and are based on my subjective experience. I think it boils down to there being a real relationship between us as collaborators and colleagues. Actual back and forth conversation. And keeping the communication lines open. Don't underestimate the power of phatic communication: a simple "got it" or "thanks" can contribute greatly to an illustrator's peace of mind.