Those are all good ideas. I've used a slightly different one: put my characters in a room. Specifically, I try to take secondary characters and have them encounter each other outside the main character. They might share a drink, experience an encounter or crisis (a secondary one), argue politics or religion ... the main thing is to open things up. Too often, secondary characters seem to exist only in relation to the main character, serving only the plot. This makes them feel shallow. It doesn't have to be just two--it can be three or four of them.
That's a really good idea! And also clever to have them interact with groups of people, as opposed to just one-on-one because that always changes the dynamic as well.
Let me know if you try any of these, and how they work out for you!
Check out the article here!