Instructions
Fly to Goldenrod City.
Walk south out of the city onto Route 34.
Walk into the house with the red roof.
Talk to the old lady behind the counter. Give her the two Pokemon you want to breed.
Ride around on your bike for a while. For every 256 spaces you move, there is a chance your egg will be born.
Head back to the Pokemon Day Care. If an old man is standing out front, talk to him to receive your Pokemon egg.