You can go straight through the grass or you can head to the beach to the left to battle the running youngster there.
Youngster Billy(Prize Money: P96)
From the beach, head to the north and you'll find an empty house. There's nothing to there right now so just ignore it. Outside the house is an old man and his pet Wingull. You can scan his pet to add the encounter to your DexNav. To the eastern side of the house, you'll find a boy whose Pokemon is really tired. You can give him one of your Potions.
Further north of the path, you'll find a couple more berry trees. You can harvest x2 Pecha and x2 Oran Berries from them. Follow the path to the west where another trainer is waiting. Defeat him and leave to the next area.
Rich Boy Winston(Prize Money: P960)