Methods of getting Shinies known so far:
If you wanna take the long way, run around in the grass and encounter a few THOUSAND Pokemon. You're PROBABLY bound to find some shinys in A FEW HOURS. >>
IF you wanna take the shorter way, buy 100 or more Max Repels, use the Pokeradar in a patch of grass where there's no Trees or anything covering any grass, and if none of the grass luckily sparkles, use the Max Repel, and run around in the places that didn't shake till you can use the Poke Radar again. Rinse, repeat.
If you wanna take the DREADFULLY LONG way that requires a whole assload of luck, simply hatch Pokemon eggs. That's right. The Odd Egg in Crystal has a 50% chance of being shiny, But other than that it shows: SHINY POKEMON ALSO COME OUT OF EGGS. The gender and shinyness of the egg is decided the second you get it, so you can't use the following method for it....
If you wanna take the longest way out there, but the most bragging-rights giving one, right before you get your starter/encounter a legendary, save. Then, when you get your starter/encounter said legendary, just Soft Reset (L+R+START+SELECT) until the starter/legendary is shiny. BUT REMEMBER, THE PICTURE YOU SEE OF THE LEGENDARY/STARTER BEFORE YOU BATTLE/GET IT IS NOT GOING TO TELL YOU IF IT'S SHINY.
Red Gyrados. A famous shiny since Gold and Silver. Well, SHiny Magikarp are easy to ome by (SO i've seen....) just fish with the old rod for a few hours.
Ways to know you will/have encountered a Shiny:
https://www.youtube.com/watch?v=XvLAz_PrY94That video shows all the stages. The Pokeradar, and what the sparkles look like. The different color, and the super obvious opening to the battle.