A major part of the process of organizing an intervention is agreeing on a goal. Know what actions you want the person to take. Do you want the person to seek help or attend rehab? Do you want them to see a counselor or join a self-help group? Make sure you have an end-goal in mind, around which the entire intervention will be structured. At the end of the intervention, you'll need the person to make an immediate decision as to whether or not to accept treatment. To do this, the person will need to be presented with the agreed upon course of action -- the goal.
Whatever the goal of the intervention is, all friends and family members should agree on it in advance. They must present a "united front" and remain focused on the same objective at all times.
If necessary, make arrangements before the intervention to help meet the goal. For example, if a treatment center is desired, choose one ahead of time and make arrangements for the person to attend. It will be easier for your loved one to take the next step to get help when everything has been prearranged. Don't forget the details, such as handling childcare if necessary, since these details could become possible reasons for objection to treatment.
Lastly, be sure the addict understands what the consequences will be if he or she does not follow through and seek help or treatment, or relapses. Like the goals of the intervention, everyone should agree on the consequences ahead of time, as well.