With a heckload of luck. Aside from the Red Gyarados in Gold, Silver and Crystal, there is no guaranteed way of getting a shiny Pokémon. There's a one-in-OVER-9000 or so chance of getting one, so you just need to get lucky... --McDlakii Talk! 07:54, 5 May 2009 (UTC)
You can also use the Poke radar to dramatically increase your odds. When you start getting longer chains with it, you may see a patch of grass sparkle instead of rustle. FOR THE LOVE OF GOD GO FOR IT, as a shiny is there.