Vaporeon: Evolve Eevee normally
Jolteon: Evolve Eevee normally
Flareon: Evolve Eevee normally
Espeon: Set Eevee as your buddy, walk 10 km, then evolve it during the day
Umbreon: Set Eevee as your buddy, walk 10 km, then evolve it at night
Leafeon: Use a Mossy Lure Module, then evolve Eevee near the PokéStop
Glaceon: Use a Glacial Lure Module, then evolve Eevee near the PokéStop
Sylveon: Earn 70 hearts with Eevee as your buddy, then evolve it
Vaporeon, Jolteon, Flareon: Rename Eevee to Rainer, Sparky, or Pyro once each for one guaranteed evolution
Espeon: Rename Eevee to Sakura for one guaranteed evolution
Umbreon: Rename Eevee to Tamao for one guaranteed evolution
Leafeon: Rename Eevee to Linnea for one guaranteed evolution
Glaceon: Rename Eevee to Rea for one guaranteed evolution
Sylveon: Rename Eevee to Kira for one guaranteed evolution