Complex sentence: He studied journalism at Columbia University and authored eighteen works of nonfiction, fiction, and poetry, before beginning his film career in the early 1930s as an MGM publicist and assistant to David O. Selznick.
Split into simpler sentences: He studied journalism at Columbia University and authored eighteen works of nonfiction, fiction, and poetry. He began his film career in the early 1930s as an MGM publicist and assistant to David O. Selznick.