fingers crossed is a wish for good luck. The middle finger is crossed over the forefinger of the same hand. In Britain people give a V-sing by holding the middle finger and forefinger apart like a V and curling the other fingers and the thumb into the palm is held outwards the sign means 'victory' if the palm is tuned inwards the gesture is rude and offensive. In the US people use the V-sign with the palm outwards to mean'peace' but the rude version is not used. Giving somebody the finger[=holding the middle finger straight up and curling the other fingers into the palm] is used instead.
Drumming your fingers,i.e. tapping them repeatedly on a desk or table, suggests impatience.
Scratching your head suggests you are not sure what to do. These gestures may also be a sign that a person is nervous
When somebody waves, one arm is raised and bent slightly and the wrist is shaken. You wave when saying goodbye to somebody or as a greeting. In Britain children sometimes wave to trains hoping that the driver will wave back. In the US children hold up their fist and move it down when a truck approaches, hoping the driver will sound the horn.