Man greeting Man - Men shake hands when greeting one another while maintaining direct eye contact.  A firm but fairly brief handshake is the norm. With friends, a simple hello will suffice.  If you have not seen someone in a long time or with good friends, a hug is common. Most men will opt for a half-hug with a macho-like back slap. 

Woman greeting Woman- At a first meeting, women generally shake hands while maintaining direct eye contact. With friends and people that you see often, a simple hello will suffice.  If you have not seen someone in a long time, a hug is common. 

Man greeting Woman- At a first meeting a regular handshake will do. With friends and people that you see often, a simple hello will suffice Good friends may engage in a light hug.