Some things. Not all the things:
Challenge the brief. Find the real problem you’re solving. Often it won’t be the one the client shows up with.
Have you seen a similar problem somewhere else? Could what worked there work here too?
Manage expectations. (The client’s, the agency’s, your team’s, your own.) Budget and time are constraints. Creativity can bend reality—but there’s a breaking point.
Don’t let your thinking become constrained. Look up, feel into it, go off on tangents. Find the “logical” solution. Consider its opposite.
Have other people poke holes.
Learn to write like lightening. Fast, yes—but more importantly: Electric.