Instructions
Travel to either Route 13, Route 14 or Route 15. Walk around until you encounter a wild Chansey. Capture it with a Pokeball or use a Pokemon with the move "Thief" to steal the "Lucky Egg." Encountering a Chansey holding a "Lucky Egg" is extremely rare. Chansey has a 1 percent encounter rate in the wild and there's only a 5 percent chance of that Chansey holding a "Lucky Egg."
Remove the "Lucky Egg" from the Chansey and attach it to the Pokemon that you want to receive more experience points.
Battle other Pokemon and defeat them. When defeated, they will yield 1.5 times the normal amount of experience points.