Most organic things can be box-modeled easily. This means making a box and extruding it until you get the form you like. Anything that I box model usually starts from the feet and goes up. First of all, you'll need a reference picture of the dog you want to make from the front and side, so you have a guideline. Make sure you only do half of the body at a time so it is symmetrical. Sometimes you may want to use the mirror tool to see how your model is doing, so I suggest using the real-time mirror there. Anyway, for a dog, you would most likely start from the front paw and extrude your way up to the chest. Once the chest is shaped, extrude the body and back, then do his hind leg. After all of that is shaped you should then make the head and shape that as you like. Then you can finally use the 'Object>Mirror' function to make you dog whole. Also, while modelling try your best to stick to quads until you're finished. Once you're completely finished, you should make two models, a fully quad(original) for backup and then make a triangluated version, because for games, it is best to stick with triangles.
I hope this helped
