Common conventions in sci-fi films include plotlines that keep audiences interested through time travel or conflicts between good and evil forces. Settings like space create suspense by removing familiar cues like sound. Many films also feature threats that endanger human civilization, like alien invasions in "War of the Worlds", keeping viewers engaged through tension and shock. Additionally, iconic soundtracks are used to set futuristic tones or indicate dramatic scenes through memorable theme music, as seen in the famous "Star Wars" score.