Instructions
Place the egg into a slot of your party. Location within the party does not matter since an egg cannot battle.
Add a Pokemon to your party with one of two abilities: Flame Body or Magma Armor. This will help speed the hatching process by keeping the egg warm.
Travel to a route that is long and runs from east to west. This location is a personal preference on the trainer's part.
Ride the bike back and forth along the route until your egg hatches. With the Flame Body or Magma Armor Pokemon in your party, this will cut the number of steps you have to ride in half and speed up the hatching process.