you can pretty much skip any movie that doesn't feature thor or captain america. For some reason all the movies they appear tie into the infinity saga or are referenced heavily in other movies. The other movies i noticed don't or get recapped enough that you know what happened without watching.
Iron Man 3 for example, nothing in that movie gets mentioned ever again. Dudes undergo name changes and costume changes only for them to be back they way they were before in their next appearance. Things that would supposedly have lasting implications are totally ignored and retconned in the very next avengers movie.
versus Cap, the smallest easter egg in Cap 2 will turn out to be a major plot point in Civil War which will in turn effect the origins of characters movies.
Or Thor might have something happen to him the needs to be known, in order to understand his status and relationship with other characters at the beginning of other movies.
Guardians: Skip, nothing in their movies is important to the overall plot of the saga except for certian relationships which get rehashed in Infinity War and End Game.
Dr Strange: Skip Thor 3 serves as a better intro for his character as he is supposed to be mysterious anyways, plus it makes him seem both more powerful and less nerfed at the same time. weird way to put but i'l explain after you've seen them.
Spiderman and Black Panther are both good and they both tie into movies that took place before them, but realistically leave them in the same place they were before both movies started, so those are optional.
Antman weirdly enough ties in very strongly to the overall plot with both movies, even though it doesn't seem very important.