Sonic's head is a circle, and to start out just draw the guidelines for his face.
in step two we begin drawing his muzzle, make sure to curve so that the eyes will fit. Then add the nose, which looks like a bean kinda.
now we add the eyes and some detail to the muzzle. The happy face has a mouth that that loolks like an upside down D. The unhappy fce has just a frown. Also make sure you know how low the "brow" goes the happier, the higher it is, the madder, the lower it is.
In this step we finish the brow and add the eyes, then we start what will become his top spine, and add the ears. Also on the mad face make his temple bulge, for effect
Now all that's left is to clean up the faces, and finish the spines, now I want you guys to know that I kind of messed up on the spine length, the middle spine should always be the longest. Remember, practice makes perfect. If you have any requests, on pretty much anything, from dragons, to anime, to sonic/ mario characters, please feel free to ask.