Usually, I start with a brief or article and I’ll read it through a few times, making doodles in a notebook as I read. Then, I spend a couple of hours in complete quiet with my sketchbook going over every possible idea I can think of, combining ideas, and looking for visual metaphors. I write down lots of keywords that I think are important. Then, I might just think for a bit and see if a fresh idea pops up. I work out a lot of my sketches in my head before I ever draw anything. If I like a concept, I’ll then try drawing a rough sketch. Once I get a few roughs drawn, then I move to my tablet and start sketching those ideas in a way that my client can understand. I often put on music when doing this part. Usually instrumental stuff: soundtracks, etc. Once I get started on the final stages of making the image, I don’t need to focus as much so I put on movies, audiobooks or podcasts that I can enjoy while I draw.
Take a break from work, if I can. Do something completely different. Go outside, take the dog for a walk or read a book. If I can’t, and need to meet a deadline, then I just sit there and push through.
Sometimes interesting things happen if you just keep at it, even when you feel like you don’t have any good ideas.