Good communication skills are essential. This person should seriously question much of what the group members say. This strategy will force the group to take a second look at every decision that is made. Having been a part of many groups myself, I believe that the best way to avoid Groupthink is to have an understanding and awareness of it. Groups that constantly question decisions are likely to never encounter Groupthink.
Groups are useful and necessary in many situations.
They often solve problems that individuals cannot. Groupthink can limit the value of groups. Groupthink problems can be recognized by identifying a set of characteristics including an illusion of invulnerability, self censorship, and others. Janis recommends many strategies for avoiding Groupthink. Groups can assign the role of critical evaluator to each member, divide into subgroups, invite experts to sit in on meetings, and so on.