Out of the mouths of babes. Fresh eyes and all that.
Even if your initial inclinations are just poorly formed hints at where you think the brief is taking you, blink, and scribble it down. Channel those early brainwaves into a envelope and then limber up and embrace the big think. (Mail it to yourself if you like.)
Should you later find yourself later wallowing in plannerly procrastination or overcooking the thinking, those first sparks may guide you back to earth. Perhaps think of that envelope as a time-capsule. Open it up once the campaign is in the can and see how far those virgin thoughts traveled.