It is easy to establish contact with warmth, affection and an interested expression. Be open, receptive and friendly and keep up the small talk! Here are some easy steps on how to greet the people that you meet in a sincere and open way.

Note: As it stands, this article is fairly specific to an informal greeting in the US.

[edit] Steps

Approach the person.
Say "Hey, how's it going?" or something similarly friendly.
Shake hands.
Start a conversation if you like. The person might be your friend if you have a lot in common with this person.
The polite way of meeting someone is:
- Say, "Good Morning/Afternoon/Evening. It is nice to meet you."
- Shake hands
- Ask, "How are you?"
Find small talk topics. To continue the conversation, make small talk remarks about the weather, family, how far you travelled, where might be good spot for lunch etc. It isn't about making yourself appear really smart, so don't sweat the small stuff. It is about making yourself affable, personable and approachable. Keep it simple.
If you are new to this person, make sure you know they want to meet you too, otherwise the consequences might lead to them getting annoyed.

[edit] Tips

Always have a smile and speak clearly and most importantly, look them right in the eye.
If you are greeting an adult, smile politely and say hello.
If you don't know the person's name, say "nice to meet you" or "nice to see you again".
Or, you can ask them politely, by saying, "It is good to see you again, unfortunately I have forgotten your name." It may seem a touch impolite, but it is a lot better than saying the wrong name.

[edit] Warnings

Don't be over-confident as it is off-putting.
Don't approach someone who does not want to be approached (look for their body language towards you).
Keep in mind that greetings vary by culture. While the generic Western conventions have become widespread enough that a hand offered for shaking will not be misinterpreted, be careful of the more subtle differences. For example, in Asia people draw a different line between ``eye contact and ``staring.