Tell someone to "Have a good day" at the end of a conversation, when you're about to leave:
A: OK, well it was nice talking to you.
B: You too! Have a good day.
A: Thanks, you too. Bye.
This is a friendly, polite phrase that you can use with almost anyone.
Use "Have a good day" in the morning or afternoon. In the evening, you can say "Have a good night" instead.