Try watching them like you are a fly on the wall. You aren't feeling what the characters are feeling- you are observing the events.

And if you can't, or don't like doing it, that's fine! I have trouble understanding characters and getting into their heads. I don't really like watching character-driven movies. I felt awful about it and thought there was something wrong with me. But then I realized that art is subjective and there's no problem skipping character studies and watching plot and spectacle focused movies.