I rarely begin a design project with a specific image in mind. What I typically do is make shapes until something makes sense; lines, circles, boxes, etc. with brushes, pens, and the multitude of mediums available at Sketchbook. I'll do color enhancing and add effects along the way by sending it back and forth between Sketchbook and PSE.
During that process, I'll periodically show the image to my wife and send it to a few people: "Does this look like anything to you?" Depending on their responses is how I proceed.
Twiddling My Thumbs
When I began making shapes and editing this one, I thought it looked kinda froggy—wasn't sure what to make of it. This is how it evolved from a blank canvas to 'froggy' by brushing some green shapes on a red screen and sending it back and forth to PS Express:
By adding layers and coloring over existing patterns, you can do things like brush additional designs without damaging the original pattern and then just delete the template layer. That's how I did the lip. Those white lines were my original guides after I saw a frog.
"One"
Then 
"Two"
"Three"
"Four"
And Then it Was
Thumb War!