Place potatoes in crock pot on the bottom followed by carrots.
(I prefer to slice the roast into about 2" thick slices at this point so that it gets better heated).
Combine flour and cajun seasoning (or whatever seasoning you prefer) on a paper plate or bowl. "Roll" or otherwise coat roast in mixture, similar to the way you'd flour fried chicken.
Place roast in top of crockpot.
If adding optional green beans, add them at the same level as roast, so that they, along with the roast itself, can get steamed during the process.
Pour chicken broth over top of the roast to help disperse the flour/seasoning. Cover crockpot and turn on low for 6 to 8 hours until roast is pretty much falling apart.
During the procedure, you might stir the roast, and if the roast settles towards the bottom, that's ok because it'll put the roast down into the liquid and help keep it moist.
If the crockpot seems to be a little dry for your tastes, feel free at any time to add a second can of chicken broth (I prefer chicken because it's not as heavy as beef broth).
The real purpose of the broth is to provide a gravy while boiling the potatoes at the bottom of the pot and providing steam cooking for everything else. As it comes along, the steam from the liquid will condensate and provide more water.