You did a very good job, but let me tell you what you should work on.
-Use thinner lines. Thick lines may be easier, however they look cheesy.
-Make the forehead higher, emphasize the shape the of the skull and add a cheekbone.
-Unlike cats, dogs do not have pointed low snouts however they don't stick straight out. Give it a bit of an angle to make it more realistic.
-The snout should be narrower, shorter and a bit rounder.
-Dogs have very small eyes.
-Emphasize the bone structure, especially the shoulder bone which is very visible compared to most bones.
-The rib cage sticks out more, and where the rib cage ends it tucks in.
-The body should be much less longer.
I hope it helps. =)