Guten Tag

This is the standard German greeting appropriate for formal and information situations. You can always use it. It literally means 'Good Day.'

Hallo

Obviously very similar to the English 'Hello,' but Germans usually use this for answering the telephone rather than in person settings. You would probably want to use one of the other greetings mentioned here for any in person meetings.

Wie geht’s?

This means 'How is it going?' A very common and general greeting, but one probably more suited to less formal settings.

Wie geht es Ihnen? uses the formal 'you' and would be the most formal way of asking this question when interacting with people you don't know.

Wie geht es dir? uses the less formal dir to be used with people you are familiar with.

But note that Germans actually expect an answer to the question. You ask this and you will get a substantial answer how it is indeed going. You can use this the way it is commonly used in English. If you don't response or ask the other person Wie geht's without giving an answer yourself, you might come across as rude.

Alles klar?

Everything alright? However, this question is more a common greeting in German than in English.

In English a question would used to express concern for the person you are talking to - perhaps because they appear upset. In German, the questions doesn't have this sort of implication.

Alles Klar can also be used as an answer to Wie geht's and the other forms of 'How is it going?' mentioned here.

Wie läuft’s

Another way to ask how is it going in more informal settings.

You also can be more specific about what you are asking about.

Wie läuft’s die Arbeit? (How is work going?)

Wie läuft’s es in Dresden? (How are things going in Dresden?)

Conclusion

Now you have a few new ways to ask people how is it going when you meet them. You've learned which greetings are appropriate depending on the formality or the settings and who you are talking.

Just remember, Germans are often a very straight forward people. If you asks question, you will probably get a real answer to the question you asked.

Auf Wiedersehen!