1)When you meet someone regardless when, say "안녕하세요 (안녕). That's common."
2)When you say see-ya in the morning,
좋은 하루 보내(보내세요.) Have a good day.
점심 맛있게 먹어(드세요) (**If it's almost lunch time) Enjoy your lunch (time).
3) When you say good-night, as Pascal said,
"잘 자 (안녕히 주무세요)"
"좋은 꿈 꿔(꾸세요)" Have a sweet dream.