Good question! The process of smoothing Dipper was a long but rewarding one :) When I finished sculpting him, I smoothed as much as I can with my finger and tools (raking method), then I went over it with 91% alchohol with a brush to smooth it further. This was the result after baking.
After baking came the fun part; sanding! I used a combination of wet sanding and steel wool in order to sand and polish this guy. First, I primed him then sanded, rinse repeat, rinse repeat! This is a photo of one of the earlier stages of sanding (I later fixed his left eye to make it more symmetrical and hair)
When I sanded this guy to my liking, I finally went over it with one last coat of primer. Primer not only gets the figure ready for painting, but actually smooths the figure as well! This is the final photo of Dipper after hours of sanding. See the difference?