How do you say...?
Good luck next time!
How can I tell someone good luck next time? What are the usual way Japanese people express this?
Here's the only way I can think of:
Tsugi ha ganbatte kudasai!
Great question - I think that's the expression I would use (We do use "ganbatte" very, very often, don't we?! ).
If the listener looked to be disappointed/tired/depressed, you can say "Tsugi ha umaku ikuto iidesune!" - it has a connotation of "Better luck next time".