I you haven't seen
DOF Master yet, it might help you get a sense for how narrow the DOF can be at 1.8, or even 3.2, at short focal lenghts.
In your pic, it seems that you focused on the dog's nose? If so, then about 1/2 of the area that's in focus is in front of the dog, and therefore of no use. By foucsing on the eyes (might be tough with all that hair!), you'd be sure to get the eyes in focus, which is almost always good, and parts of the face in front of and behind the eyes would be in focus too.
Practice is key. What you posted is a good shot. Don't be too hard on yourself!