what makes a good film trailer

things that makes a good film trailer are very good sound effects such as very dramatic and loud noises to cut out plus diegetic sounds like foot steps or radio station transitions can be very effective a film you can see this in is REC in the scene where they hear foot steps and banging coming from above, another good technique for film trailers is ambient sounds these are like birds, crackling twigs etc a good film that shows this is james bond goldeneye at the end of the trailer where james bond jumps of the dam into the river and you can hear the waves in the background