Speak first. Speak often. Psyblog brings the answers:
Crucially, though, the study showed that not only did a leader’s dominant behaviour of itself encourage others to see that person as competent, but this was true even though their suggestions to the group were no better, or even worse than others. In reality the leaders did not always make the best contribution to the task, but their voices were usually heard first and most often.
This study suggests leaders emerge through more subtle processes than the word ‘dominance’ might imply. Rather than brow-beating or bullying others into submission, leaders-in-waiting effectively signal their competence to the group by making greater verbal contributions to discussions. Others then assume that their greater contribution will mean their group will be more likely to succeed.