First I tested different letter forms with my Pilot Pens to find the best shapes.
Next I outlined every letter in Adobe Illustrator to find the best curves. That was actually a bad idea—I'd better started with outlining them in font editor.
The quest for the best 's':
Then I crafted outlines in Glyphs App (font editing application). I redrew every letter even though they were outlined in Adobe Illustrator.
At this moment my trial of Glyphs App timed out. I am not sure I should pay almost $300 for the app I won't use much. Though the app is good ;)