Alder is waiting right by the Pokemon Center, but he wanders off after you approach him. Take this opportunity to heal up your Pokemon, too.
In the house directly to the right of the Pokemon Center, you can talk to the old man in there and he will give you a Potion.
Head on over to the north part of town and you'll run into Alder again, who wants to help train you. He'll notice you have two Town Maps and then mentions he saw a Trainer with a Tepig on Route 20, which is, of course, Hugh, the guy you want to give the Town Map to. Alder then points you in the direction of Route 20, which is just off to the east.