To get the perfect attacking Pokemon in Omega Ruby and Alpha Sapphire, you'll need a Pokemon with high IVs (Individual Values), and the best way to get one is through breeding.
Thankfully YouTuber ToyDualer has a guide you can check out below on breeding in the games.
IVs cover elements such as HP, attack, and Speed, and range from 0 to 31. There's nothing you can do to change a Pokemon's IV stats but you can have some control over them through breeding.
Complete the game and get up to the Delta episode, which means you'll have access to the best daycare centre in the Pokemon series. You'll also need the Destiny Knot item, this passes five of the parent Pokemon's IVs down to the baby Pokemon in the daycare centre, greatly speeding up the breeding process. The five IVs passed down are randomly selected.
Another item you need is an everstone, which prevents the Pokemon holding it from evolving. The baby Pokemon will always have the same nature as the Pokemon holding the everstone in the daycare centre. You could also use a power item, which will see the associated IV passed onto the baby (e.g. a power item to boost HP will raise the baby's HP too).
The video talks you through finding these elements and everything else you need to know for successful breeding in the games.