Complex sentence: When working on "Out of this World" Shubik had made a valuable contact in John Carnell, a key figure in British science fiction publishing, founder of science fiction magazine "New Worlds" and agent for many of Britain's science fiction writers.
Split into simpler sentences: When working on "Out of this World" Shubik had made a valuable contact in John Carnell, a key figure in British science fiction publishing. He was the founder of science fiction magazine "New Worlds" and agent for many of Britain's science fiction writers.