Put everything in the crock pot together, including the little seasoning packet that usually comes with the corned beef. Put on high for an hour or so till it starts bubbling a little (simmering) then on low for about 8-10 hours. It will be tender and delicious and not cooked to death.
Forgot to say put corned beef in first, then veggies then cabbage on top and enough water to cover beef, potatoes and carrots, Cabbage doesn't have to be covered, it will steam. You don't mention cabbabe. If you con't like cabbage, then leave it out.