Whatever it was you were doing, Fly to Mossdeep City. Heal up and stock up there before heading south onto the ocean. Surf southward to Route 128.
Here, simply Surf east towards Ever Grande City; you should’ve fought everyone here last time you were here, so it’s pretty easy sailing.
Ever Grande City
Go east and north to the waterfall and climb it with well, Waterfall. Heal up in the Pokémon Center at the top, then go north a bit using the Dowsing Machine to find a Revive a bit to the west of the Pokémon Center. From there, go north, and onto the Victory Road .