You probably already know the phrase "Good luck!", which people say to cheer someone on. You may also know "Good luck with (something)":

Yeah, good luck with that.

But people also say "Good luck in ___" or "Good luck at ___" when a person is leaving to move to a new place:

Good luck in Delaware!

Good luck at your new job.

You choose whether to use "in" or "at" based on what words follow it:

• "in" Boston, France, Australia
• "at" school, your new job