Use language that is commonly used in conversation

The closer to a human agent’s language you can make your application sound, the more usable it will be. This is not a call to try to fool the user into thinking that they are talking to a real human being. Rather, it is a modest suggestion to avoid having the system speak say things that a human being would never say in normal circumstances. Don’t be tempted with formal, cramped language, or language that reads nicely but would never be spoken by a socially competent human being.

Here is a bad prompt:

System: Please tell me the date of your birth, including the month, day, and year.

Here is a better prompt:

System: What is your birthday?