Spiderman Homecoming is an example to me of showing way too much. By the time I got done watching the trailers, I already knew the plot, and that Peter would go through a problem, and Tony Stark stating you have to be better, important quotes or statements that should be kept away from the trailers, along with them having to save people upon the boat in pivotal moments.
They’re guilty of it as well,and Homecoming was one of the trailers that came to my mind instantly.
Certain trailers in the past for me that did a great job was like the original Alien, to Inception to Godzilla 2014. Godzilla 2014 trailers were some of the best in recent time imo, because within those teasers, they Never showed you Godzilla outright with only shadow glimpses along with a good pace that simply made you hyped for it.