Vaporeon: Use a Water Stone on Eevee
Jolteon: Use a Thunder Stone on Eevee
Flareon: Use a Fire Stone on Eevee
Espeon: Raise Eevee’s friendship and level it up during the day
Umbreon: Raise Eevee’s friendship and level it up at night
Leafeon: Level up Eevee near a Moss Rock or use a Leaf Stone in games that support it
Glaceon: Level up Eevee near an Ice Rock or use an Ice Stone in games that support it
Sylveon: Raise Eevee’s affection/friendship and teach it a Fairy-type move, then level it up
Eevee: Do not evolve it