as a general rule no, so many trailers spoil a movie by showing important scenes out of context. Comedies giving away the best jokes is often a culprit of this. Then there's showing a scene from the end of a film, or sometimes a scene that doesn't even make it to the final cut.

obviously they have to market movies somehow, but i like the idea of a short prequel instead of a trailer, like Covenant has done. Gives you a flavour of the film without giving anything away. Or the whole online thing which The Blair Witch Project exploited so well. The Deadpool 2 trailer that was posted on TE awhile back was another example of how to make a good trailer but not spoil the film.