Don't evolve Eevee
Vaporeon:
Water Stone
Jolteon:
Thunder Stone
Flareon:
Fire Stone
Espeon:
Level up to any level when Eevee is at tuktok happiness at daytime
Umbreon:
Level up to any level when Eevee is at tuktok happiness at night
Leafeon:
Level up Eevee one level near the Moss Rock in Eterna Forest
Glaceon:
Level up Eevee one level near the Ice Rock on the path to Snowpoint city. (While going north, stick to the right of the path and you will get there)