Subhanallah the greetings between Muslims are very meaningful, they are prayers for peace and Allah (s.w.t) blessings and mercy on each other. The Quran advises us:
When a courteous greeting is offered to you, you meet it with a greeting still more courteous, or (at least) of equal courtesy. (4:86).
Also, different cultures have different customs on how people greet each other. These may include shaking hands, hugging each other, or kissing each other on the cheeks. However, it is important that individuals of the opposite gender avoid physical contact unless they are mahram (closely related). Men and women that are not closely related can simply exchange vocal greetings.
The Holy Prophet (saws) advised us that when visiting another individual's house, the visitor should greet the people of the house from outside by saying, As-salaamu-alaikum. If the visitor receives a reply and is invited in, they may enter. If a visitor does not receive a reply the first time they may repeat the greeting up to two more times. However, if they don't receive a reply by the third time they should respect the residents' right to privacy by leaving the house.
With all the resources of communication modern society provides, this advice of the Prophet (saws) can be understood to mean that we should phone, (or text or e-mail the other person if appropriate) to see if it is convenient to visit. When we arrive at their house we should ring the doorbell or knock at the door to inform them of our arrival and wait for the answer.
Muslims must also greet one another if they sneeze. If a Muslim sneezes, they should say Alhamdulillah which means: "All praise belongs to Allah (s.w.t)" hearing the sneeze others should say : "Yarhamukallah for a male or Yarhamuki-Allah for a female which means: "May Allah have Mercy on you" and the person who sneezed should answer: Ghafara Allahu la-na wa la kum, which means: "May Allah (s.w.t) forgive us" so even when we sneeze, Muslims pray for each other.