The most obvious way to identify which bass is which is by its mouth. The upper jaw of the largemouth bass extends beyond its eye, unlike the smallmouth bass. Another key give away is there is a dark greenish stipe horizontally on the largemouth and the smallmouth has vertical green brownish lines across its body. Generally both fish are found in the same location, smallmouth tend to prefer colder water but they can both be found in the same lakes. Catching either one of these would be considered a good day of fishing and preparing one of these is relatively easy.
picture can be found at http://reelriveradventures.com/wp-content/uploads/2013/06/Bass_ID2.jpg