How do you catch Ditto in Firered?

First get hm surf,then you have to go to pallet town. use surf and keep going straight until you get to Cinnabar island.go inside the Pokemon mansion.go to the top floor.walk around for a while.soon you will run into a ditto!
Go to fuchsia city. Then in one of the exit/enter doors with the guard,He wont say im thirsty or anything like that. Then there should be 2 rows of grass left and right. Then a ditto may appear. Some oddishes might appear before Ditto. Then you catch it! Good luck,Fellow trainers!