When I sketch dogs or animals that are on the move I often will photograph with my phone along with watching them in person. This way I can freeze different positions, analyze movements and hopefully better capture the animal. I usually start my sketch with pencil and then once I am happy with my lines I can either start to paint at that point or use my pen and redefine the line and then paint. I do it different depending on how I feel, either works. Try both and see which way your prefer. Here is my first outline sketch, done while Gumby was doing his laps.
Gumby has cataracts so his eyes were not overly clear, I used artistic license to improve his eye. I wish it were as easy in real life.
Here he is, the owners really loved the sketch, so I cut it out of my sketch book and gave it too them. A gift for the gift they gave to this little dog of much love, care and attention his last few years here.