You can use greeting to open a conversation and use leave-taking for closing.
4.Responding to Initial Greeting
§Good morning (until about lunch time, or before 12 a.m.).
§Good afternoon (12 – 6).
§Good evening (until about 9 p.m.).
§Good morning, Sir.
Note: Do not use “Good Day”, except in Australia.
3. Initial Greeting
§How are you?
§How’s it going?
§How are you doing?
4. Responding to Initial Greeting
§Very well, thank you and how are you?
§Very well, thank you.
§Not too bad, thanks.
§Ok then …
§I’ve got to go now.
§So, I’ll see you next week.
§I think I’d better be going now.
§Well, it’s time for me to leave.
§I think it’s already late at night.
§I must be going home.
§Bye-bye; Bye; Bye now; See you. Take care.
§See you later---Fine
§See you soon---OK
§See you tonight---All right
§Good night (after 8 p.m. or retiring to bed)
§Do not use “Good evening” for leave-taking, use “Good night”.
§Goodbye John, and all the best (to someone who’s leaving for a long time).
§Goodbye Peter, and good luck (to someone who’s leaving for a long time).
This expressions could be seen here.
See also this video.