If you want your meat to be distinct cubes rather than strings, lessen the cooking time. If you cook the stew for less time, you may also need to add some flour to thicken the gravy. Take out a 1/4 cup of the cooking liquid, stir into it a 1 tablespoon of flour and then incorporate this back into the stew. Stir until gravy has thickened. Also, I like my meat in big stringy chunks, but if you prefer smaller pieces, cut the meat into 1/2 inch cubes.