Instructions
Travel to Jubilife City by biking, walking or by using a Pokemon that knows the move "Fly" to automatically transport yourself to the city.
Enter the Jubilife Television Station and speak with the attendant at the bottom of the second floor. He will tell you that day's lucky number. If the lucky number matches the Pokemon ID of any of the Pokemon in your possession, you will win a prize.
Match three digits with the lucky number to obtain an EXP Share. You can increase your chances of matching three digits by trading Pokemon with several different people as the Pokemon caught in your game have several of the same digits associated with your game file. As different game files have different digits, you should have several different Pokemon in order to try to obtain an EXP Share.