When you draw a comic strip, if you're going to wait for inspiration, you'll never make it.
Here's 4 1/2 minutes of a 1963 documentary on Charles Schulz, with some good advice about getting ideas:
His advice — about becoming professional enough to sit down, and deliberately come up with ideas at will — is true.
When people who are not cartoonists find out that I am a cartoonist, they will often say how wonderful it must be to be creative all the time. Sometimes I nod and agree, but really, the truth is that it isn't wonderful.
It's a job.
It's a job I love, but it's real work.
To produce regular, consistent, commercial work requires discipline. Even if don't feel funny that day, or you don't feel "inspired," the work has to be done, you have to market it, you have to pursue the sale.