The most important, but often the trickiest, aspect of being promoted through a management structure is continuing your personal relationships with colleagues. People who previously enjoyed chatting or gossiping socially with you, and perhaps even privately venting frustrations about management, may feel uncomfortable with your change in status. You will also probably feel that the kind of informal relationship you previously enjoyed is no longer appropriate.
An important leadership skill following a promotion is therefore to maintain positive relationships with those staff, whilst moderating your behaviour to ensure that you effectively establish your new level of authority. Keeping those relationships too close and informal risks undermining your authority, making it difficult to manage those people. It could also lead to resentment amongst other staff, leaving you open to claims of partiality or favouritism. However, abandoning past friendships entirely can also cause bad feelings in the office, alienating staff and reducing morale. The best approach is one of open honesty, you can (and should) still be friends, but you both have to accept your new seniority.
As you’re promoted, delegation skills will also become more important. Increasingly, you will have to trust staff to make their own judgements and decisions whilst working towards the goals of the business. This can be difficult for managers who have been used to taking control of every task, but it’s vitally important to show that you have confidence in your team.
When there’s multiple tiers below you, you’ll also have to understand how to manage managers, and how to demonstrate good management techniques by example.