There's nothing more intimidating to an advertising writer than a blank sheet of paper, or a blank document on a computer screen.
Young and Rubicam, one of the best advertising agencies, once ran an ad showing a pencil whose point was on fire. The headline read, "You're only as as good as your next ad." That's what's so scary.
The solution for me is to write something. Anything, just to get over that hurdle. Then keep on writing --- more headlines, more word-thoughts, puns, idioms, and ideas. Lots of them, to come back to later and evaluate. I said later, not now. Hold all judgement in check. Later you'll surely find something to love, change, or build on.
About this point in the conversation, writers' block usually comes up. It's enough to burn a hole right through a creative director's duodenum when, a week after getting the assignment, a copywriter announces "I just can't think of anything good".
One writer once verbally attacked me with, "What do you think I am, a machine?"
Usually it means the writer is too tough on herself. Lots of thoughts and ideas, but none "breakthrough" enough. The better the writer, the more likely that will happen. It also can mean it's good but the kind of thing the writer's been doing for years so successfully. That's too easy for her, and not different enough.
Once all this is explained, the problem usually dissolves.
The people who need creative directors the most are the creative directors. They often succumb to the Peter Principle of being promoted to a job they're not good at ("I'm too busy managing to make an ad"). Or they think everything they come up with is great and precious. This is false.
In addition, because advertising is an art, not a science, nobody can positively predict whether an ad will be a success. This is also crazy-making.
Ultimately, every advertising person has their own secret weapon against the challenge of a blank sheet of paper. Mine is quantity.