I guess it's dexnav.
-Bring a lot of max/ super repels, elixir, ether, leppa berry, HP restoring items and pokeball.
-Equip your shiny charm.
-Get some Pokemon with false swipe, paralyzing or sleep inducing move, sweet scent.
-Make sure you have nothing on the day you'll be chaining.
-If there's multiple patches of grass, move to the middle.
-Sneak, don't walk or run.
-Don't run away from a Pokemon, get to battle with a trainer and don't leave the area.
-Have a Pokemon with sychronize in front of your party.
If a Pokemon runs away, the chain will break, you will need to restart the chain.