Without PokeRadar or breeding foreign pokemon, you can't. You're stuck at 1/8192 chance.
Even with those things above it's still very very rare. You should stop trying and just play the games, you will get a shiny eventually.
I have only ever seen 3 shinies in all the hours I have played on Diamond, Platinum and HeartGold. Managed to capture Wingull and Silcoon but shiny Unown got away from me :(