A. Every day

When we leave someone we usually say Goodbye and also perhaps See you soon! See you soon is quite informal.
When someone goes to bed, we usually say Goodnight. We sometimes also say Sleep well.
Don’t say Goodnight when you arrive somewhere, only when you leave.
If you ask for something you usually say Please.
If someone does something nice for you, you say Thank you or Cheers (informal).

B. Special days