Do: Add in an exciting new villain
Star Trek: The Motion Picture isn't as bad as its reputation suggests, but the Enterprise crew's first cinematic adventure suffered from a serious lack of tension... possibly because the villain was an energy cloud. What a difference a great villain makes: Ricardo Montalban's miles-over-the-top sneering villainy in Star Trek II: The Wrath of Khan redefined the series for the big screen.
See Also: The T-1000 in Terminator 2: Judgment Day, Ralph Fiennes' Voldemort in the later Harry Potters, Lee Van Cleef in The Good, The Bad, and the Ugly