For information on how to start an ADD twelve step group, I refer you to the ADDA Support Group Leader Training Manual, which contains excellent materials on this subject. The answer to this, of course, will depend on your unique circumstances. If you anticipate large numbers of people an educational group may be best. If you already have a small sharing group that has been meeting for some time, the members may be ready to go on to a skills type format. It is important, however, that you stay flexible and in tune to the changing needs of members.
Many successful groups are actually hybrids of the different types of structures.
For example, it can work very well to begin with an educational type group to provide a large membership base and pool of volunteers. Often, these groups serve as hubs for a network of smaller sharing, skills based or twelve step groups. The larger educational group refers members to the small groups. Sometimes this is done within a single meeting, with time set aside after the general program for breaking into small groups. I wish you all much success as you form, reform or maintain an ADD adult support group.