He who would write humorously should spend an hour at Walmart people-watching. She who would write creatively might wish to do the same thing, preferably with laptop or phone in hand for note-taking.
Anyone hoping to write creatively and freshly should take the advice of movie-maker Harold Ramis. “I tell students (on arriving at a party or similar type gathering) to identify the most talented person in the room. And if it isn’t you, go stand next to him.”
Absorb. Listen. Remember. (And above all, be quiet. You’re there to observe.)
I’ve heard of a workshop for creative thinking among executives where the participants play paintball for an hour, then brainstorm on some topic. They are given a stack of magazines of any and all kinds and given 30 minutes to find every creative slogan or motto, and to jot it down. At the conclusion, they are thrown into small groups and told to adapt the best of those mottos to their own industry.
Creativity can be manipulated. The juices can be made to flow.