Formally? Just a firm, hearty handshake with a smile and a bit of eye contact. I try to only glance at their eyes and then focus more on the bridge of the nose, I think it's less imposing that way and people seem to like it. Informally, I like fist bumps. They're quick, easy, and you don't have to get another person's sweat and germs on your hands. With my best friend? We lean past each-other, raise one leg, and shake ankles