Don't do everything yourself
There are so many aspects to being responsible for a team of people that the first skill to learn as a manager is to accept that you cannot do everything on behalf of the team.
This also connects back to being flexible and adaptable. Giving yourself permission to not do and complete everything. You should let some things be, and you should occasionally even let something fail, because that can be a liberating experience and a catalyst for better performance and effectiveness – for both yourself and the team.
Similar to starting a new job at a new company, as a newly promoted manager, your natural tendency will be to take on everything, including challenges where others have perhaps failed; work long hours; attend more meetings; talk more; act more like a manager; and generally, take on the world!
This is comparable to the adrenaline rush of an athlete. That initial surge is useful to get you starting out of the blocks fast, but not so useful in the long run. It's certainly not sustainable and can actually be counterproductive in situations where you need composure, calmness, coolness, and clarity of thought.
As the leader of a team, your actions and behaviors set the tone, as well as the boundaries of what is acceptable and unacceptable. You are the example of what is positive and benevolent, as well as negative and malevolent. With this in mind, remember when you were still a developer working for a manager. What exemplified a manager's leadership that was useful to you as a member of their team? Were they frantic, obsessive, and compulsive about every single detailed task? Were they sluggish, dawdling, or indecisive? Or perhaps they were somewhere in the middle and variable according to the situation?
In my experience, finding that middle ground is vital, especially at the beginning of your journey, or at the very least, staying away from being at either end for too long. There may be a time when being more obsessive and devoted is required in order to get an important migration absolutely perfect, or a time when dawdling and being more easy-going is required to enable creativity and unconventional ideas to surface. The key is to be conscious of where you are within the spectrum and deliberately behave in the appropriate way to yield the desired outcome.