First impressions are very important. So, if you want to make a nice, natural start to a conversation, you should carefully choose the words you use. There are a numerous things that influence how people greet each other, but according to research*, the words or phrases we choose to say hello are influenced the most by age, gender, and formality are social setting (formal vs. informal).
One study into the words and phrases that are spoken most often in American English found that there were common patterns in how native speakers begin a conversation. The study concluded that the top 3 tips to saying hello naturally are:
1) hi is the usual and most frequent greeting in spoken American English, hey is a more casual form and hello seems to be more frequently used when you want to show respect to someone.
2) First names were common in casual situations, but more formal terms of address* (for example, Mr Jones) are used in more formal settings. Last names are also commonly used when speaking to someone significantly older.
3) If a greeting question (how are you?) is posed*, it is usually answered with a short reply that gives little real information (E.g. A: How are you? B: Fine), or just repeated without an answer (A: How are you? B: How are you?)
Greeting a person is the best way to begin a conversation, so next time you want to talk with someone are you going to say Hi, hey, hello or how are you?
* terms of address: 呼びかけの言葉
* posed: 提示される
*Rydblom, Oskar. 2014. You still say hello!: A corpus study of the greeting words hi, hey and hello in spoken American English. Linnaeus University, Faculty of Arts and Humanities, Department of Languages.