I always look grim, unless someone in the band plays a bum note, or one of the dancers falls over. Luckily Kate, the lead singer and fiddler in the band I play with, has a completely natural-looking smile which she can deploy effortlessly when playing fast fiddle tunes. A knack I wish I had, but will never learn. My advice is, dont force it. If it looks like a mad maniac's grin. or Joyce Grenfell, leave it out.