Well theres something called the masuda method which includes to different ways. Through breeding (which is way to difficult to do efficiently in gen 5) which is that when 2 pokemon from different countries breed, the chance for a shiny is higher. Also, I think shiny pokemon who breed are slightly more likely to have shiny babies but not sure about that.
The other way is a way im not sure about but I do know you go into a bush that is at least 5x5 and have plenty of repels and the poke radar. Also you cant
leave the grass or use a bike and make sure you avoid non shaking bush battles with repel. Just walk and keep walking into the shaking bush. Doing so will
break your chain and you will have to start over. Keep chaining with going from shaking bush to shaking bush and you will eventually find a shiny but it may take a while.
hope that helps
Much Doge. Wow