I can list a few things that I do here...
One thing I do frequently is put my right finger on my chin and either look up and to my left for a moment, or look at the person in front of me and nod slightly. Sometimes this is accompanied by me holding out my left hand to the side and moving my left index finger up and down, especially if I'm trying decide what action to take or remember how to get somewhere. Once I've decided, I put my right hand down, and point that left finger straight up for a second before acting.
I've also noticed that if I'm thinking about saying something, I'll tend to put my right index finger on my lower lip, and then as soon as I start to speak my right index finger usually points towards the person or people I'm talking to for a second, and then as I speak, I show my hand with the palm open as though I were giving them something, and then tend to flex my fingers slightly as if I were accepting something if they respond with something I agree with or understand. But if I disagree or don't understand, I usually wince a bit, turn my palm down, open my mouth slightly, put my left index finger on my lip and begin flexing my right index and right ring finger up and down a few times while gazing upward. And then when I say something else, I usually offer my right hand again, but this time my fingers are usually shaped as if I were holding a ball rather than simply being offered flat. If they respond in a way I understand this time, I usually put my right index finger on my lip again, with my left hand touching just below my neck and above my chest, and I nod before returning to the initial style with a flat hand.
Note that I don't do any of this consciously, but I remember them because those are the most common. I've noticed that I do others like these less often, but I can't recall them at the moment. One other thing I've noticed is that people who don't speak English as well can usually understand me better if I have both hands free, and can let myself do these things.