Mistralton City

Head to the Pokémon Center in Mistralton City. Heal your Pokémon and purchase items if desired.

Exit the Pokémon Center and head east to enter the red house.

Talk to the girl inside the red house to receive an HP Up.

Check the bin in the south-west corner of the red house to find an Iron.

Exit the red house and head west, then follow the path north of the Pokémon Center.

You will be stopped by Professor Juniper. Talk to her; she will check your Pokédex and give you a Master Ball.

Shortly after, Skyla, the Mistralton City Gym Leader, will appear and speak with Professor Juniper and you. Professor Juniper will then leave.

Skyla will speak with you and then leave for her Gym.

Head east from the T-intersection to enter Route 7, or west towards the runway.

Go to the large building known as the Mistralton Cargo Service, which also serves as a control tower.

Enter the Mistralton Cargo Service. Talk to the woman next to the main counter to receive a Sharp Beak.

Move to the north-east part of the room and talk to the man behind the counter. If you show him a Flying- or Psychic-type Pokémon, he will reward you with a Net Ball.

Head onto the runway. Go south down the eastern side of the runway.

Move east along the south side of the parked plane to find TM58 - Sky Drop.

Move back to the runway and continue south to the bottom.

If playing Black 2, move between the center-left and bottom-left greenhouses. If playing White 2, move between the center-left and bottom-left plots of soil. Find a Max Repel obscured by the greenhouses or plots.

Move back onto the runway and go up the western side.

You will reach a female Backpacker. Talk to her.

Continue north until you find two small planes on the runway.

Use your Dowsing MCHN halfway between the two planes to find a hidden Flying Gem.

You can now choose to enter the Mistralton City Gym to challenge Skyla or head east into Route 7 to train.