If you are wanting to improve your Umgangssprache (colloquial speech), then Mach’s gut is a very popular German expression that will make you sound like a real local.
Typically used as a parting phrase, this German colloquialism is often said in an informal manner between good friends or perhaps even close colleagues.
When you next meet up with a circle of friends who you know well, just as you are about to go your separate ways you can wish them “Mach's gut!” which is comparable to the English expression “Have a good one!”. The literal German translation means “make it good”.
Contrastingly you would not use the phrase in more formal situations, such as in an academic setting with a lecturer or with someone you should show respect such as a friend’s grandparent. The phrase can often be exchanged for the more formal “Auf Wiedersehen!”
Using the phrase in a sentence, you could say:
‘Bis morgen, mach’s gut!’
See you tomorrow, have a good one!