I recently filmed my first (really) short film with a couple of friends who had experience in theatre and improv but not filmmaking.
From my experience with that I can say that I definitely understood how to tell them what I needed from them better and how to decide on what to ask to get the best results because I've been an actor in their position before.
I think that when you're working with an inexperienced actor, your best bet is to just write your character for them as much as you can. It's best to just let them be as honest as they can be.
So yeah, I think it helps a lot to try lots of different roles.