Strong main characters are important, but having memorable minor characters can be a huge boost for the overall strength of your story.
That doesn't mean they need to have deep backstories or anything - you can't really go too in-depth into a character if they only appear in one scene, after all - but you can still use some simple tricks to make them pop out, like:
A quirky trait
Being a good foil for the main characters to drop great lines
Being designed purely to make this a stronger scene
I think Shane Black does this expertly in Last Boy Scout, and that movie is worth a rewatch to help you punch up your minor characters in your second draft.
