Mash two Pokemon with favourable IVs and hope for the best. Actually not even joking.There should be an IV guy in the game that tells you where to what specific IVs your Pokemon has.
A 6 IV Ditto would be ideal for breeding. I'm not too far in Sun and Moon to know how to get Dittos and such yet. So someone could help you with that.
Basically this. Here's a few extra notes:
- Ditto can be found in the wild at Mount Hokulani. If you chain them long enough you can get Dittos with 4 IVs which currently is the best available without hacking them in.
- There's an Ace Trainer at a post-game area called the Battle Tree who will unlock IV judging for you, at which point you'll be able to check out the IVs of each mon in the PC, you won't have to withdraw them and take them to a specific guy anymore. Super helpful.
Other than that, yeah. Mash together mons that have good IVs and hope for the best.