Natalie Goldberg, who wrote the how-to-write books Writing Down the Bones and Wild Mind, encourages her students to write constantly. And she says every once in a while a student will ask, “But what do you do with what you write?” She answers, “I don’t know. What do you do with after you drink a glass of water?”
She means that you don’t have to do anything with it. It becomes a part of you. Maybe there’s a line or two you can use. Maybe a whole paragraph. Maybe nothing. But it’s not wasted effort. You write because you’re a writer. You art direct because you’re an art director. You come up with ideas because you’re creative.
So don’t be afraid of generating ideas you won’t use. Experiment with layouts. Write long body copy for a visual solution. And then you’ll be able to decide what, if anything, to do with them.