Generalize the big shapes and forms. Trees in a landscape can become verticals. You can look at Georgia O’Keeffe’s abstract drawings and paintings of form as inspiration. There are many others of course. Arthur Dove. Andre Derain. Braque. You probably have a list.
Organize an image into just one element of art (line, shape, color, value, texture, space). How you do it depends on your interests. It’s doesn’t have to exclude all the other elements, just consider one a dominant feature. The more constraints you use, however, the better. Try to be as severe as you can.
Use a photograph or group of photos with the intent to transform them. I was amazed and shocked by seeing some of photographs (see below) that Paul Nash used for his great painting Totes Meer or The Dead Sea, 1940. Notice it’s not a copy, he’s using bits and pieces.
Image: courtesy The Tate.
For more photographs: https://bbm.org.uk/airmen/NashTotesMeer.htm