Eevee must have high friendship or affection
Level up Eevee during the daytime
Make sure Eevee does not know any Fairy-type evolution conditions that would trigger another evolution
In games with location-based evolution restrictions, avoid areas that force a different evolution
In Pokémon GO, evolve Eevee after earning 10 km with it as your buddy and during the day, then ensure it is your buddy when evolving
In games with nickname evolution, use the nickname Sakura once per save file if available