well, I'm the fondant newbie around here but I'll share what I've encountered.
Cornstarch comes off of fondant easier than p.sugar. With either of them, I use a clean kitchen towel to wipe down the fondant when I'm done rolling it. I do the wipe-down before I put it on the cake.
I think getting mine smooth looking is more luck than skill!
I'll step back and let the real fondant experts share their die-hard tips and tricks!