Instructions
Keep Eevee in your party at all times and go on long walks. Just being with you will slowly increase its happiness.
Use expensive vitamins like Protein and Calcium as well as berries to make the Eevee like you more.
Avoid giving Eevee bitter items to eat, as they will make Eevee start to dislike you. Energy Root, Revival Herb and Energy Power are examples of bitter items.
Bring Eevee to Veilstone City for a daily massage. The Massage Lady is located in a home near the Veilstone Gym.
Use the Friendship Checker application on your Poketech to see the happiness levels of the Pokemon on your team. Tap Eevee with the Nintendo DS stylus. If two large hearts appear on both sides of the Pokemon, you are ready to transform it into Umbreon.
Level up Eevee at night once its happiness level is high to have it evolve into an Umbreon. The numerical level of Eevee and the location where it gains a level do not matter, as long as its happiness level is very high.