The hand should not be closed, which would be suspicious, but relaxed and cupped, just the way your hands would naturally be if they were at your sides and not holding anything. It can also be a good idea to give the hand that's palming the card something to do like holding the deck, or a drink, even a spectator" arm or shoulder, or if you are standing or sitting at a table you can casually lean it on the edge of a table. When the hand that is palming a card or a coin is holding or doing something, it helps greatly in warding off suspicion.