Nice job tracking and getting the blur in the background.
The light looks to be late or early day coming from the left, because of this puppy's butt is rather nicely lit but unfortunately his face is in shadow. Pay attention to where your light is coming from and what you want to light, puppy's butt is awfully cute but I'd prefer to see the face
Composition wise, you have some room for pup to run into but chopped the tail, zooming out a bit would give a little extra room. The corner of the patio stone is distracting, catching pup out further in the lawn would be better.
The shot would benefit from post processing, colours are kinda blah and need some balancing, saturation and contrast adjustment to make it really pop.
Hope this helps, you have a gorgeous subject there
Thank you very much for the tips there, it's always refreshing to have new perspectives on shots! The lighting in Denver right now casts pretty substantial shadows all day. I'll definitely touch this up a bit when I get back to my other computer!