Mmmm...I love making pot roast in the crock pot.
Cut up two potatoes into chunks; cut up carrots into chunks. You can use celery, too, if you want. Put it in the crock, then place the beef roast on top. Add 1/2 cup water or beef broth. The rest of the seasonings, I don't measure...I just eyeball it. I add Worcestershire sauce (a few shakes...how ever much that is!), salt, a bit of pepper, garlic powder, onion salt, celery salt, and oregano. I've kind of played with the seasonings lately...that's what I added last night.
Cook on low for 10-12 hours.