Qualifications and education
A sofer should be religiously observant, of good character, and knowledgeable about the laws concerning sofrut. It is a common misconception that one has to be a rabbi in order to become a Sofer, which is not required by Jewish law.
People who want to become ritual scribes usually learn from another expert scribe by undergoing Shimush (Apprenticeship), since it would be impossible for someone to be a scribe without any actual practice. The hardest part about learning to be a Sofer is not the calligraphy, but rather remembering the thousands of laws that apply to Sifrei Torah (Torah scrolls), Tefillin (Phylacteries) and Mezuzot and all the other texts that are written on parchment.
Some people who want to become ritual scribes learn at the Vaad Mishmereth STaM with the option of receiving a certificate. (This is an international organization whose goal is to protect the halachic and artistic integrity of the scribal arts. It is located in Jerusalem, and in Brooklyn, New York.) Certification of this sort is not a halachic requirement, nor does it necessarily guarantee the quality of a particular sofer's work. This process does however ensure that a certified sofer has received the proper education and is a recognized expert in the field of sofrut.
http://en.wikipedia.org/wiki/Sofer#Qualifications_and_education