I just rolled out some gumpaste and cut out a letter using a sharp kitchen knife. Is there a way to clean up the edges and get them really smooth? I tried, but I couldn't get it as smooth as I would have liked.
Once they are dried you can use a nail file on them
I have the best luck doing like kakeladi says. If I try when it's freshly cut out, I end up with a mishapen piece. You could try a dry soft paint brush and smooth them gently.