Since pokemon Diamond and pearl there has been a feature called poke radar chaining. Esentially what that means is you use your poke radar in a patch of grass and then go to it. Then you do it again, hope it's the same pokemon,hope it's not a decoy and then do it over and over again.
There are many ways to end a chain such as getting a different pokemon and getting decoy grass. Eventually at a chain of 40 the chanche of finding a shiny is 1/200. If you find a shiny while poke radar chaining the grass won't shake but instead it will be shiny and have sparkles on it.
You can get the poke radar? on the 2nd floor of the pokemon lab in lumoise city after you beat the game. You just go there and talk to professor sycamore's assistant

But since X&Y there has been a new method called chain fishing. It is essentially the same thing but with fishing.
It is also easier to do if you are in a rock formation when there is a rock behind you and on both sides. Or if you fish on a shore.
I find it easier because it is harder to mess up.
The only ways to mess up are moving from your spot, not reeling in a Pokemon (helps if you have a Pokemon with sticky hold or suction cups),
and reeling in to late or early.
So catch a gulpin or inkay for sticky hold or suction caps to almost always reel something in.
You are allowed to get different pokemon and are allowed to run away unlike poke radar chaining.

I have gotten a shiny clauncher by doing this and I hope i find lots more.

I have to correct you on something. The chances of getting a shiny patch is 1/200 not 1/40. You should also explain Chain Fishing a bit more. I know what it is but others might not so you might want to change that too. Other then those, there's nothing wrong with the post.

sedo45 : Just edited it. What else should i put about chain fishing.
Also, sorry about the 1/40. I accidentaly read yesterday that it is a 5/200 chance, not 1/200.

Also, after 88 pokemon i got a shiny chinchou.

mourinhosgum :
You said it's kind of like pokeradar chaining. Some people might think they have to get the same Pokemon each time. We know this is not the case. Some may think they can't run away even though they can. I realised it wasn't much but still.

I know both Poke Radar and Chain Fishing like nothing but wastes of time that are only useful for boring you to death, but they are not. Apparently, shinies are more likely to appear while using them! So do it !