Catch Eevee
Use a Glacial Lure Module at a PokéStop and evolve Eevee while near it
Rename Eevee to Rea before evolving it once for the guaranteed Glaceon method
Evolve Eevee with 25 Eevee Candy after meeting the Glacial Lure Module requirement
Check for special event methods if Niantic is offering one at the time
Make sure the Eevee you evolve is not already nicknamed if you have used the name trick before