Obtain a Rockruff with the Own Tempo ability
Level Rockruff up to level 25 or higher during in-game dusk time
Make sure it is in a game that supports Lycanroc Dusk Form
Evolve it only at dusk, not during day or night
In Pokémon Sword and Shield, use a Rockruff with Own Tempo and evolve it at dusk
In Pokémon Ultra Sun and Ultra Moon, evolve Own Tempo Rockruff at dusk
In Pokémon Scarlet and Violet, Lycanroc Dusk Form is not normally obtainable through standard evolution methods