Unfortunately, you asked two questions, so I had to edit out the second. Of Mice and Men, by John Steinbeck, is a novella which lends itself quite easily to a movie. The characters, action, and dialogue of the novella are all perfectly suited to the big screen.
While Steinbeck does an excellent job of creating each of the unique characters in this work, seeing them come to life will make the story even more poignant. This is especially true of the two primary characters, George and Lennie, since they are so different both physically and mentally. Seeing the giant of a man with the mind of a child is much more powerful than reading about him, for example, and the contrast between them is quite striking.
The action of this story is also suited for the movies: cowboys (ranch hands) on the move; an arrogant but insecure ranch owner who likes to assert his authority even when it is not necessary; a giant man who likes to pet mice, puppies, and other soft things; an accidental and tragic murder; and the horrifying realization that the kindest thing George can do for Lennie is kill him. Watching George and Lennie dream about their own place, with rabbits, and then seeing some of the other misfits in the story join the dream--and then lose it--is sure to mean more heartache for the viewer of the story than the reader of this story.
Finally, the dialogue is also suited to the movies. While it is written effectively, it can seem a bit artificial to a modern reader.
“I ain't got no people. I seen the guys that go around on the ranches alone. That ain't no good. They don't have no fun. After a long time they get mean. They get wantin' to fight all the time. . . 'Course Lennie's a God damn nuisance most of the time, but you get used to goin' around with a guy an' you can't get rid of him.”
Listening to these men (and one woman) say their lines in the dialect Steinbeck intended would be a perfect accompaniment to the story which plays out on the screen. The novella contains realistic dialogue which will transfer well to a movie.
Some adaptations of the movie have already been made, and I linked the site below.