To make your Pokémon level up faster, I'd suggest lucky eggs (easier to find in ORAS on Pellipers) for a 50% bonus, Pokémon-amie (I think you only need to get to the first heart for a 10% xp bonus), experience O-Powers (use on other players to level them up more frequently) for up to a 100% bonus, and if you have a second game you can get an additional 50% bonus for training the Pokémon over there. When I was finishing up training, I relied on triple battles at Cafe le Wow in Pokémon Y - only needed one O-Power for all of the battles. The Elite-4 is about the only thing that comes close in ORAS, though.