Way 1 · best default
Good luck
Short and natural before any test, interview or challenge. Add "with" for the thing.
Examples
Good luck with your interview tomorrow!
Good luck today, let me know how it goes.
In a conversation
A: My driving test is at nine.
B: Good luck! You'll be fine.
Common mistake
Not: I wish you good luck in your exam.
Say: Good luck in your exam!
"I wish you" makes it sound formal and stiff, like a speech. Friends just say "Good luck!"
