Any artistic endeavor, is, at it's core, one thing, and one thing alone...communication. The most important skill for any artist to develop and nurture is the ability to express their ideas. Now, you can do that any way you want, speech, words on a paper or computer screen, paint on a canvas, but you have to be able to convey something to the people around you.
Jackson Pollock is my favorite painter, hands down. He works in the realm of the abstract. Yet he's still expressing a mood or emotion in a vibrantly clear way. Blue Poles, Number II gives you an entirely different "feel" than, say, Lavender Mist, Number 1. (Computer images do not do these works justice.)
When you enter the realm of a collaborative art form, theatre, or film, or music, this skill becomes even more vital.
I'm starting work on a comic book project with an artist. We spent a lot of time just throwing ideas back and forth, and honestly telling each other our thoughts. We came to an understanding about the storyline, in a broad sense, and the look of the project. Things can, and will, change and adapt, but he and I have now come to a starting point where we both understand what we're trying to achieve. I can think about it while I'm working on the script (which I better get on, the "deadline" is Saturday), and he can think about it working on the visuals.
The goal is clear, and it gives us freedom to play around with our own parts in the enterprise. Anything I come up with must move us toward the target we've set. The concept we've agreed to explore. Music can work in much the same way.
When you talk theatre or film, things are a little different. This artist and I are forming a partnership, it's just us, and we are equals. When you enter into a theatrical production, for example, your director is your leader, and they are tasked to bring your concept, your goal, to the table. They provide the ultimate vision that the actors and tech crew are there to support.
Unless the artist heading the project can effectively share his or her views about the work they are trying to make, the entire team will feel lost. This vision is what keeps the project on track, and drives it to it's goal. The goal, of course, is to share that vision with the eventual audience, but how can it be effectively conveyed to them, if it's not effectively conveyed to your team?
I've worked on productions that land on both sides of the line. There's nothing more frustrating than feeling lost because either you can't understand what your director is going for, or they can't. Likewise, when your director can answer questions from a strong central idea, the rest of the process becomes smooth as silk.