Step 1: Give 6IV Ditto Destiny Knot and breed it with your desired Pokemon
Step 2: Breed the Pokemon that breeded with a Ditto, give it a Destiny Knot, then Breed it with that selfsame 6IV Ditto
Step 3: Keep doing Step 2 until you have a 6IV version of your desired Pokemon.
You can check the Pokemon's IVs at the Judge. In ORAS, he is in the Battle Resort Poke Center, and in XY, he is in the Kiloude City Poke Center.
In Gen III, he is behind the Battle Frontier Poke Center, in Gen IV, he is in the Battle Tower, next to the PC, and in Gen V, he is in the Gear Station after you reach the Hall of Fame.
Hope I helped :P