Hi, 

Sometimes, when we need to greet somebody, we just use the most common greeting, Hello/Hi, How are you? Fine, thanks. And you?. It is already time to put into practice other greetings. Click on the picture below and you will learn more English greetings in both formal and informal situations. 

Another useful link with 17 useful English greetings 

                                                                   Informal or formal greeting? 

It’s a good idea to wait until someone speaks casually with you before you speak casually with them. You may find that people will begin to use casual greetings with you over time, as you get to know each other better. Formal greetings are also used when you meet older people.

                                                                   Useful expressions at a glance

                                                                 American and British English