Instructions
Get the Trainer Counter app after you receive the PokeRadar from Professor Rowan. To get the Trainer Counter enter Pal Park and talk with Professor Oak. He gives the app to you when he sees that you have the PokeRadar.
Buy as many Super or Max Repels as you can afford. Stock up on multiple types of Poke Balls so you are prepared to catch a shiny Pokemon when one appears.
Go to any grass patch, and stand in the middle of it. Use one of your Super or Max Repels. This keeps away lower-leveled Pokemon. If you encounter a Pokemon other than the type you are chaining, you lose the chain and must start over.
Use the PokeRadar. Several grass patches around you start to shake. If the shaking grass does not glow, a normal Pokemon is hiding there. If the grass glitters and shakes, a rare Pokemon is hiding in it. Grass that does not move much, but flashes white, hides a shiny Pokemon.
Walk to any patch that is four patches away from you in any direction. Fight the Pokemon that appears to battle you. Kill it or catch it, but do not run away from the battle. Running away breaks the chain.
Walk to another shaking grass patch. If you do not see a shaking patch, take a few steps around the area, then use the PokeRadar again.
Keep fighting the same type of Pokemon to build your chain. Tap the "App" button on the bottom screen to switch to the Trainer Counter app. This lets you see what your current chain is.
Use more Repels whenever the current dose wears off. Pokemon that know the Intimidate ability also ward off weaker Pokemon. If you have one on your team, move it to the first position in the party. This is useful if you run out of Repels.
Stay in the middle of the grass as often as you can. If you walk too far to the edge of the grass, you may lose the chain.
Continue fighting the same kind of Pokemon until your chain reaches 40. Use the PokeRadar to reset it. Look for a patch of grass the glows white two times. Walk to the patch to catch a shiny Pokemon. If you don't see a glowing patch, keep using the PokeRadar until you do.