First up; head into the Pokémon Center found near the entrance to the town. Heal up and check the Pokémart if you need to. Once you're done; head to the west side of the center and talk to the man by the screen. He'll give you TM66 - Payback . Head back outside.
Head east and enter the building there. Head to the second floor and go to the last room of the floor. You'll find Mr. Bonding here as usual. This time he'll give you a Speed Power . Cool! Afterwards he'll leave. You should too.
Back outside; head east and north into the fenced off meadow. Head around to the back of the building and you'll find a partially obscured item which turns out to be a Timer Ball . Head back to where the Pokémon Center is and head north from it. You'll come upon a Team Flare Grunt singing to himself who will then walk off.
From there, move north to the junction and head west. Follow the path until you reach the fence. From there, head south along it until you reach the item, Soft Sand , in the corner. Head back north and you'll reach a building. Head inside. Talk to the woman near the beds to receive an Everstone .
Tip #024: Delaying Evolution
When a Pokemon is about to evolve after a Level Up, you can press the B Button to stop it evolving during the evolution animation. There are some benefits to not evolving - the main one is that non-evolved Pokemon learn moves faster than their evolved cousins. In most cases, you'll want to evolve ASAP to benefit from better stats.
Head back outside and east back to the junction. Talk to the girl wearing a beret nearby and she'll head to the hotel. Head back there and find her on the west side of the ground floor. Talk with her to find out some interesting info. Head back outside back to where you spoke with her.
Continue north along the path and you'll see another path leading off east. Head down it and you'll see a Photo Spot. Feel free to make use of it. Don't try to head out of town by the east exit just yet though, especially without healing your Pokémon first. Instead; head back to the main path and head north until you reach the monument.
You'll see a house that you can enter behind it. Do so if you want to; but there's nothing very important inside. Now head back south and then west to get to the very west edge of the town. Head north and as you're near the exit there, the Team Flare Grunt will walk out of town. Now head on out of town after him!
You'll find that you're at a dead end. Where did the Grunt go? Weird... Anyway; head back into town. Now; make sure you've healed up then try and head out of the east exit. When you try to leave you'll be stopped by the Gym Leader Korrina from before and she'll challenge you to a battle. Quite random so be sure you're ready before hand.
Trainer Battle: Leader Korrina
So apparently that didn't count as beating the gym leader; but okay. You'll probably want to heal again too; so do that then actually exit out of town.