As far as my designing goes, I usually sketch out an idea. Depending on both time and how comfortable I am with an idea in my head, I may take a design to color or just idea of colors, and final sketch or not.
For instance, I felt pretty comfortable with the ballet cookies I had done a little while back so rough sketches were all I did. Just an idea of what I was going to do and most of the actual design work came literally as the icing came out of the tip!
But for a "Jake and the Neverland Pirates" inspired set, a little more design planning was involved.
These were all first drawn out very loosely, but maybe I spent too much of my past career in Clean-up but I just had to tie them down some more. It really isn't time lost since I then cut out the sketches, taped them to index cards and popped them in my KopyKake.
The treasure chest had a little sketch with a rough idea but I had to draw up a larger one since I hand cut the dough. I just then "improvised" as I decorated. :)
Again, since I still and probably will always feel most comfortable with a pencil, I like taking most of my drawings as far as I can. Much easier to erase a drawing than to scrap off icing and start again. Having said this, sometimes it's impractical to draw everything out before decorating a cookie- but then again, some really cool things happen when you just go with the "icing" flow!