You're going to need 2 kinds of pokemon (Aside from what Torinnnnn said)
Smeargle with False Swipe/Spore
And Quagsire with Damp ability (Or any mon with Damp Ability)
Then you're going to need lots and lots of pokeballs that you want your shiny in.
Also pokemon like Oddish can learn Sweet Scent naturally, so if you wanted, you could have your Smeargle Sketch Sweet Scent if you don't want to carry Oddish around.
Then pick a pokemon you want shiny go to the area and hunt for it.