Like most animation you need to create the character in different states of running. So use a program that lets you layer and re-edit your dog.
Start off small with the beginning state and the end state of the running dog. Save those two images and add them to the GS animate attribute (these would be frames now). See how that looks - probably jerky.
Now the more 'frames' you add in-between your start and finish state the more natural the animation will look. 30 frames would be ideal for natural looking but depending how your game shows it just start at 8 frames and go up as you see fit.
Remember also you would most likely be looping this to show the constant running so you could essentially re-use frames in the loop. So frame 1 to 8 woud be start to run frames and 9 to 16 would be the reverse order of those images taking you back to you first frame then it loops.
Muybridge is a great reference. There are two books, Animals & People. But there are also great books on animation that will break down the traditional cartoon animators method.
Preston Blair's "Cartoon Animation" is classic but there are others. And many of his examples are online these days.
Comments
Start off small with the beginning state and the end state of the running dog. Save those two images and add them to the GS animate attribute (these would be frames now). See how that looks - probably jerky.
Now the more 'frames' you add in-between your start and finish state the more natural the animation will look. 30 frames would be ideal for natural looking but depending how your game shows it just start at 8 frames and go up as you see fit.
Remember also you would most likely be looping this to show the constant running so you could essentially re-use frames in the loop. So frame 1 to 8 woud be start to run frames and 9 to 16 would be the reverse order of those images taking you back to you first frame then it loops.
Hope that helps.
Preston Blair's "Cartoon Animation" is classic but there are others. And many of his examples are online these days.