>>3961525Imagination is a skill/activity that needs practice and experience, just like anything else, and some people are just more inherently better at it.
My degree in illustration focused on this in the last two years of core classes. You have to learn how to think, how to explore, how to spot cliches and toss them out.
Here's how to start. Take your favorite book, or album. Design an image for the cover. Do 10-12 thumbnail ideas. Try to make each one unique. They don't have to be detailed, just the overall idea. Don't worry what others have done, or what the actual cover is. Let your mind explore ideas. 10-12 ideas is a lot of work for newbies, I struggled like everyone else in class did, at first.
Then, pick the best 2. Work those up as rough drafts. Don't worry about accuracy, or details, or reference/poses. Just get the ideas more fleshed out.
Whichever one feels the strongest, pick that, and do a finished piece. Again, don't worry if it looks like something that's already been done. Just finish your idea, get used to finishing ideas. It's a good habit to get into.
Our first project in the first class was to do that, with the phone book.
Our second assignment was to pick a phrase, like "Don't cry over spilt milk", and illustrate it. Again, 10-12 thumbnails, pick two, work them up, pick a final, finished piece. REALLY interesting what people came up with on this one.
This is the kind of exercise they'd have us do, to start thinking. That's part of creativity. If an image doesn't form in your head, take the steps to create the environment where it will. Just staring at the paper won't make it happen.
Oh - and we'd generally get these done over a week, weekend included for the finals.