Personally I give each character a face, either from a person I know who matches their personality or a celebrity that fits the description, even though sometimes it can be really annoying if the author gives more details on the persons appearance and my character doesn’t fit that lol. I’m very curious as to what other people do.
I rarely picture or cast celebrities in the books I read. A bizarre exception to that is the case of Thomas Dewey, about whom I read in Truman, and am reading in Nixon: A life. Both times I cast the late Bill Hicks as Dewey. I think Hicks would have hated to be cast as him, or not, I can’t decide.