1. Say Tasleem

The Prophet Muhammed (SAW) was asked: "Which Islam is good (in terms of action)?". He said "To feed the people and to say salaam to those you know and those you do not know." - Bukhari

2. Lengthen the Greeting

A man approached the Prophet (SAW) and saluted him saying "As-salaamu Alaykum (peace upon you)", the Prophet (SAW) returned the salutation and after the man sat down, the Prophet said: "Ten"; then another man came and said "As-salaamu Alaykum wa rahmatullah (peace and mercy of Allah upon you)" the Prophet (SAW) said: "Twenty"; then a third man came and said " As-salaamu Alaykum wa rahmatullaahi wa barakaatuh (peace and mercy and blessings of Allah upon you) the Prophet (SAW) said: "Thirty". - Muslim

3. Smile

The Messenger of Allah (SAW) said: "Do not consider any f the good things as insignificant; even if it is that you meet your brother with a cheerful face." - Muslim, At-Tirmidhi

4. Shake Hands

The Prophet (SAW) said: "There are not two Muslims who meet each other and shake their hands, except that they are forgiven before they depart (from each other)." - Abu  Dawood

5. Say Kalimah Tayibah

This includes the remembrance of Allah, supplication and saying a good word about someone for their manners, actions and character.

The Prophet Muhammed (SAW) said: "A Kalimah Tayyibah is charity". - Muslim