Generation IV introduced some of the most widely used shiny hunting methods that are still being used for their reliability and because they meet the desired results: getting a shiny Pokemon. One method that arguably gives the best results would be the Poke Radar.
In the Diamond, Pearl, and Platinum the player is given a key item called the Poke Radar after they have seen every Pokemon in the Sinnoh Pokedex by Professor Rowan, though he doesn’t go into depth for what it does. The radar is used to find Pokemon that you couldn’t otherwise find in the games (without using it). Though that isn’t its only function, the Poke Radar can also be used to find shiny Pokemon. Be warned, though, shiny hunting while using the Poke Radar is very time consuming and requires a great deal of patience as well as your undivided attention.
Now to start, you’ll need an obnoxious amount of repels (super repels and max repels are fine too, and probably preferred). You will eventually use them, believe me. It’s just better to buy too many, then not enough and have to start the process all over again (it’s happened to me, and I’m still kicking myself for it). You should make sure you have enough pokeballs (Ultraball, Nestball, Netball, Duskball, etc.) in your bag too just to be sure.
After you’ve done that and made sure you’re prepared, you can select the Pokemon you’ll be hoping to find and look up where to find it. Some people keep a Pokemon with the ability Synchronize as their first in their party so that the Pokemon’s nature (the one with Synchronize) will have a chance of being passed over to the shiny that they’re hoping to capture, though it isn’t needed. Once you get to the area where the pokemon is found, you’ll need to try to find an area where there are a large number of grass patches (try larger than 4 x 4). I normally go to the center of that patch and save the game before going any further. After that you should set the Poke Radar for your Y Button and use a repel before using your radar. Four patches of grass should shake and you’ll go into one of them, hoping you run into the Poke that you’re searching for. If it’s the wrong one, you select ‘Run’ and reset your radar by taking 50 steps, then you would use the Poke Radar again and repeat the process until you encounter the desired Pokemon. If you run into the one you want, you’ll either have to catch the Pokemon or cause it to faint. Once you do that, another set of four patches should shake and your chain has begun. Chains are made up of the Pokemon you’ve either caught or defeated that are of the same species encountered one right after another. Though if you run into another Poke besides the one you’ve begun your chain with, your chain will break and the game will act as you’ve run away.
To increase your chances of meeting the same Pokemon consistently, it’s said that you should almost always enter the patch of shaking grass farthest away from where you’re currently standing and by matching the pattern of shaking grass to the one before it. Chains that reach 40 (there’s an App on your Poketch that counts your chain) give you a much greater chance of running into a shiny and it’s recommended that you don’t exceed it unless you find a patch of grass that glows twice rather than shaking. Otherwise, you’d reset the Poke Radar by taking 50 steps (while avoiding the patches of grass that shook) and use the radar again.
Chains may break randomly at times; it happens. Or after you’ve caught your shiny, you can continue to reset the Poke Radar and try for another. It does take a while before you get the hang of it and you’ll need to be patient with yourself. If you become tired, make sure to stop playing during battle so that you don’t miss the shaking patches. And keep in mind that it does take a bit of practice before you get the hang of chaining, but hopefully you’ll eventually catch yourself a shiny by using the Poke Radar.