
Signal the transition - Make everyone, former peers, new peers and your boss aware of the impending change in relationship.
Tread lightly at first - You might have lots of great ideas but start slowly. Focus on your new role and relationships before proposing significant change.
Establish your authority - While you need to move slowly, you do need to let your former peers know you're now in charge. It doesn't have to be done in an aggressive, overbearing manner but it must be done.
Try out new roles - Take some time and experiment with different modes of relating. Get feedback and continue to evolve until it feels right.
Deal with the disappointed competitor - If one of your peers also wanted the job deal with their disappointment and potential resentment. Don't let it fester and become a bigger issue.
Make use of the advantages - You've been on the inside, seeing how things really work where the rubber meets the road. Use that knowledge to help build credibility and to avoid potential buried land mines.