Instructions
Use your bike to travel between cities and towns. Because eggs hatch after you take a certain number of steps, you can increase the speed at which you take those steps by riding your bike around instead of walking or running.
Catch a Pokemon that has Flame Body or Magma Armor as one of its abilities. Slugma, Magcargo, Magby, Magmortar, Camerupt, Ponyta, Rapidash and Moltres are some examples of Pokemon with these abilities.
Place one of those Pokemon in your party along with the Pokemon egg. This will help cut down on the number of steps you have to take -- the heat given off by the Pokemon's ability warms the egg.