Bring Pokemon that know Strength, Surf, Cut, and Flash if you want to fully explore Victory Road. Walk forward to find N. He gives you HM 05 Waterfall. It lets you scale waterfalls found throughout Unova. For example, you can now fully explore Route 14 with Waterfall. When he leaves, you can walk past each of the badge gates and the big gate. The next area has a Pokemon Center, so heal your Pokemon and stock up on healing items. Victory Road is a long stretch that will probably push your team to its limits. There are four items in the maze-like area south of the Pokemon Center: a Dusk Stone hidden in a rock, an Iron hidden near two trees, a PP Up, and a Star Piece. Enter the ruins when you're ready.
Enter the cave near the Doctor. There is a hidden Max Revive in the little enclave when you enter. Go west to find two Ace Trainers. They can be battled together or separately. The male doesn't track your movements, so it's easier to start a double battle if you walk towards him.
The item northeast of her is an Ultra Ball. There are two cuttable trees in this area. The tree in the middle of the forest is pointless, but the tree on the west side leads to a Full Restore in the southwest corner. Head to the southeast end of the forest to find some stairs that lead back to the ruins.
Walk south until you find a boulder. Move it left until you hit the crack in the floor, then move it down once, right six times, and down once. Cross the bridge to the east to find an Ace Trainer.
Hop down the ledge to find yourself back at the beginning of the ruins. You might as well heal now considering the Pokemon Center is just on the other side of the stairs. Either way, go back to the four-way path near the two Ace Trainers in the cave. This time around, take the north path to find two boudlers. Move the accessible one north into its hole and take the path east to a Pokemon Ranger.
The cave entrance north of him leads to the Pokemon League, but there are still a few more areas to explore in Victory Road if you're interested. There are also a lot more battles which will help your Pokemon level up before taking on the Elite 4. Start by going west of the two Veterans to find some stairs leading south to a Battle Girl.
She gives a Rawst Berry after defeat. Now you're at the area from earlier with the two boulders. Push the remaining boulder into its hole and use the new entrance. This new area of the cave is very dark, so use Flash to light it up. There's a set of stairs to the west and a PP Max north of it. Use the stairs to travel east. There's a Rare Candy on the other side of the small lake. Take the path north to find an exit leading back outside.
Now you're near the exit to the Pokemon League again. Walk up the narrow stairs to find a Dragon Fang, which boosts Dragon-type attacks by 20%. Use the other eastern stairs to find another cave entrance. Inside the cave, walk west down the first set of stairs and south to battle a Veteran.
Walk west down the big set of stairs to pick up a Dragon Scale, which can be used to evolve a Seadra into Kingdra when traded. The nearby exit leads to another cave entrance that's blocked by Zoroark. Keep this place in mind after you beat the Elite Four. For now, head back to the two Veterans waiting on the stairs and use the nearby cave entrance to begin a battle with Hugh.