There's no real method. However, here's a few tips:
- Recharge rate is every 50 steps.
- You need to be in a grass patch and OFF your roller blades (Switching to roller blades will break the chain).
- When you activate the Poke Radar and go into rustling grass, whatever Pokemon shows up, that's the Pokemon you are chaining for (If it's not, try again).
- To continue the chain, knock out the Pokemon and more grass will rustle after the battle. The objective is to keep finding the same Pokemon you knocked out. The more times you encounter it, the higher the chance it is shiny. Be careful for decoy patches which break the chain.
So the things mentioned are the only things stopping you. The things you need are just persistence, hope, belief, and proper knowledge of using the PokeRadar, which you probably do have. xD
Hope I helped. :)