Pokémon Ruby and Sapphire/Skill and Level Increasing Items

There are a few items that help your Pokémon grow in different ways.

The Macho Brace doubles the amount of Effort Values gained (EVs), while lowering speed in battle (only temporarily). Effort values control your Pokémon's stats, with 4 EVs equals 1 stat point. Obtainable at the Winstrate House on Route 111.
 * Macho Brace

The lucky egg is an item that increases the amount of Experience points your Pokémon gets by 1.5 times. To obtain the lucky egg, you have to catch a wild Chansey that is holding one in the Safari Zone, in FireRed or LeafGreen.
 * Lucky Egg

The Soothe Bell increases happiness gain for your Pokémon when worn. This is useful when trying to evolve Pokémon the evolve from happiness (like Espeon and Umbreon) or if you just want your Pokémon to love you. Obtainable at Slateport in the Pokémon Fan Club.
 * Soothe Bell