What were some differences between the novel and film that influenced the story, Of Mice and Men?

There are actually two film versions of this novella. One is from 1939 and the other from 1992. I'll assume you are referring to 1992.

Candy never came into the room when Lennie and Crooks were talking to each other.

Lennie's hallucination about Aunt Clara and the giant rabbit is removed.

George and Lennie escape from Weed on a train was added.

Curley has a scene where he practices boxing on a punching bag, this was added to the film.