How do you find shiny Pokemon without the poke radar?

its kind of easy but it takes a while ive been playing Pokemon platinum since mar. 22.2009 and i got my poke radar on nov.23.2009 and ive been using it for almost 3 months then i stopped and i was on my way to stark mt. to see if there was any items i missed and i got a Pokemon in the grass and it was a female raticate and it was shiny so if you try this it will most likely take a while until you get a shiny Pokemon without poke radar.