When paying or receiving change, use both hands or place items on the small tray at the register. Don't slap cash down.
The small tray (called a koin torei) is for cash exchange. Place your money on it, the cashier returns change on it. This avoids hand contact and feels formal.
Business cards (meishi) are exchanged with both hands and a small bow. Read the card carefully before pocketing it. Never write on someone's meishi.