Rinse the corned beef under cold water
Place the corned beef in the slow cooker fat side up
Add the spice packet if included
Add enough water, broth, or beer to cover the meat halfway
Add optional vegetables such as onions, carrots, and potatoes
Cover and cook on low for 8 to 10 hours
Cook on high for 4 to 5 hours if needed
Check that the meat is fork-tender before removing
Transfer the corned beef to a cutting board and rest for 10 to 15 minutes
Slice the corned beef against the grain
Serve with the cooked vegetables and cooking liquid if desired