Basically, what you need are:
- Pokemon that already have perfect IVs in some stats (Ditto isn't exactly required but it's optimum)
- Destiny Knot
- lots of time
- your Bike
- the Kiloude City judge
- a Talonflame (optional but highly recommended)
- Power items (optional)
- Everstone (optional)
To get Pokemon with already perfect IVs, you can:
- find them in Friend Safaris (this is why Ditto safaris are so coveted), as all Pokemon there will have 2 perfect IVs randomly. Ditto is just more used than anything else because it can breed with every Pokemon, so if you have one with some perfect IVs that means it can pass its IVs down more frequently.
- chaining Pokemon to a chain of 60+. I've done this myself while chaining for a shiny Furfrou, and I can say that past the 60th chain, all of the Furfrous I caught had 3 random perfect IVs. The Pokemon you can chain are limited, but Ditto is one of those that you can chain easily, since the Pokemon Village has a good patch of grass for chaining purposes. You also get the bonus of 3 perfect IVs rather than 2.
- or trade for one (but Dittos with perfect IVs are quite coveted).
While chaining is tedious and can frequently lead to nothing (due to your chain breaking), I would recommend it if you have the time, because you can get a shiny, some perfect IVs and the possibility of Pokerus. Once you get used to chaining, you can sort of do it while multi-tasking.
The Destiny Knot will pass down 5 random IVs from both parents if one them is holding the knot, meaning the baby will have a higher chance of inheriting the perfect IVs. The Everstone is optional to pass down a desired nature, and the Power items are also optional to pass down a specific IV, i.e. the Power Weight doubles EV gain for HP, and it'll pass down the parent's HP IV to the offspring if the parent is holding it while in the daycare. I remember in Gen V this only had a higher chance of doing so, not a 100% chance, but I'm not too sure about Gen VI.
Now put the 2 Pokemon in a day care and just keep hatching eggs until you get one with the IVs you want. Once hatched, fly to Kiloude city, go into the Pokemon Centre and get the guy dressed as an Ace Trainer to judge the newly hatched Pokemon. This is why I recommend a Talonflame because it has Flame Body and can use Fly, meaning it's 2 uses in one Pokemon.