Things You'll Need
Instructions
Walk through tall grass a lot, looking for wild Pokemon. This is the only way to go if you are playing a Generation II game. The odds of encountering a wild shiny Pokemon are 1/8192, so you'll be doing a lot of walking to find one.
Use the Masuda Method in generations after II. The Masuda method is simply breeding a wild-caught Pokemon from your game with a wild-caught Pokemon traded to you from a different language version. This increases your odds of breeding a shiny Pokemon 4 times, to a total of 1/2048. Even though these are still relatively low odds, this process is much more reliable than walking around looking for one. In "Pokemon Black/White" this increases the odds again, to 1/1366.
Use the "Poke Radar" in Generation IV. This item makes the grass shake where a wild Pokemon is. Knock out or capture the Pokemon and you will begin a "chain" where the next patch of shaking grass will contain the same type of Pokemon. However, you must use "Repel" items to prevent encountering a Pokemon in a non-shaking patch of grass, which will break the chain. The more members of the same species of Pokemon that you encounter, the higher the likelihood that the next one will be shiny. After a chain of 40 for example, the likelihood has increased to a 1/200 chance that the next will be shiny. This will be denoted by the grass glowing white instead of shaking.
Have a friend trade you a shiny Pokemon, and breed it with one of your own. Your odds of breeding a shiny offspring can be as high as 1/64 if done properly, breeding a shiny from your game with a shiny from theirs, especially if it is a foreign language version.