Instructions
Capture a Ralts on Route 102. Ralts will only show up rarely in the tall grass, so it may take a few random encounters before one appears. Ralts is level 4 or 5, so catching one will not be difficult. To catch one, use any status-changing moves, such as those that will paralyze or put the Pokémon to sleep.
Place your Ralts at the front of your Pokémon lineup; use him to battle Pokémon trainers and other wild Pokémon so that he gains experience. You can view the experience of your Ralts at any time by selecting "Pokémon" from the menu and then selecting your "Ralts."
Gain enough experience with Ralts to reach level 20. At level 20, Ralts will evolve into Kirlia.
Gain enough experience with Kirlia to reach level 30. At level 30, Kirlia will evolve into Gardevoir.