They partnered with outside brands
Perhaps the most well-known partnership between two brands is Audi and Iron Man. This started with fictional billionaire Tony Stark driving multiple iterations of the Audi R8, plus various other shorts featuring the German brand and key MCU characters. And this isn't just mere product placement - it's clever collaboration. Here's an example:
They asked fans not to spoil the movies
There was much hype surrounding the franchise during the release of two Avengers films - Infinity War and Endgame. And because there will always be people who will spoil others for their own pleasure, the movie casts themselves personally appealed to the public not to spoil either movies. Even the directors wrote an open letter to fans, with hashtags #dontspoiltheendgame and #thanosdemandsyoursilence going viral when both films were released.
They know their audience well
There were several movie easter eggs all over which have multiple comic book references hardcore comic geeks know, and I'm not gonna write them down individually as they take up a lot of space. Nevertheless, the universe has been around for more than 11 years now with a solid fanbase and massive fans tuning in at every film launch or events such as the Comic Con.