From time to time, advertising writers have told me they're suffering from writer's block. I usually have the same amount of empathy as I have when somebody tells me they don't have a thing to wear.
Some students tell me they can't seem to think of anything to write, usually on a day when a paper is due. The reason I have trouble empathizing is that I have never had the block, but I think I know some of the causes.
1. They can't think of anything spectacular. No "killer idea", as we say. Anything less can seem like nothing.
2. They haven't done their homework. Ideas don't fly in the windows or through revolving doors. You have to do the work first. The research, the store visits, talking to people at the factory and people on the street. David Ogilvy told my friend Ron that you have to know seven times as much as you're going to write, before you create an ad. Most copywriters don't.
3. They're tired of solving problems the same old way --- even if they're very successful at it. Creative people are their own worst critics, and that's what makes them good. It also makes for a continual striving for something new and better.
4. Something else is going on that has nothing to do with writing. I'm not a therapist, yet I feel the block in writing is often something to do with feelings of self-worth, fear of being rejected, and so on. If it wasn't writer's block, it might be dentist's block, or CPA's block.
My suggestion for all of the above is to go to work. Free associate. Think of some metaphors. Go to the library and look at books of award-winning ads, or even better, a book of cartoons.
As soon as you loosen up, so will your pen. They say the most intimidating thing to a writer is a blank sheet of paper. So fill it up --- write down everything that occurs to you, both good and bad. (Later, with a little tweaking, bad ideas can turn into good.) Put the paper away for a day, then add to it.
I say about a good idea what my grandmother used to say when I lost something: you'll find it when you're not looking for it.