In addition to John Mace’s excellent advice, I’d say that one of your primary roles is to insulate your team from interference by upper management, including unreasonably frequent demands for status updates, demands to go to some useless corporate training that has nothing to do with their jobs, requests to “take this person just for a few days” for some proposal effort (my own personal bugaboo), and so forth. That probably means that you’ll have to take on much of those efforts because your upper management isn’t going to give a shit about how important it is for your people to remain forcused on their tasks to meet deadline; they just want to show their bosses that they’re hitting their numbers on whatever, e.g. status is 75% (of something), providing support for pointless bizdev efforts, number of people who are Six Sigma green belts, et cetera. So, you’ll end up writing status reports for your entire team. Since nobody actually reads those fucking things in any detail, you can just put in the approrpriate front matter and Gantt charts and fill up the rest with chapters from Catch-22 quoted verbatim and see whether anyone is paying attention.
You also need to find creative ways to get your people the tools and training they need to do their jobs, and insulate them from criticism even when they make (honest) mistakes; in other words, you bear the brunt of criticism so that your team isn’t disrupted by übermanagers trying to “get to the root of the problem”, and have to take responsibly for correcting the problem (which is, after all, your job). It’s not the role of your upper management to be sympathetic with your team’s failings regardless of how reasonable it may be, which means you need to start out pushing back against unreasonable expectations at every turn and build a “management reserve” into every estimate of effort or cost to buffer against the unknowables that you are still expected to anticipate.
However, if you have someone who is genuinely underperforming and you’ve made a reasonable effort to demonstrate your expectations and give them the opportunity to improve, you need to move them off of your team, or at least into a role that not only minimizes their ability to damage work performance and morale but shows everyone else that you recognize that said employee isn’t performing. If you can, you should put such people through the formal performance improvement process and then show them the door if they don’t shape up, but my experience has been that neither management nor human resources will support you in this if there is any question whatsoever of legal action or other blowback regardless of how poorly the employee is performing. In fact, I would argue that human resources exists almost exclusively to protect the company from liability,not to support line managers or discipline underperforming employees, and they will only do so when forced by harassment or hostile work environment statements in writing or if senior management steps in and orders it to be so. Do not expect human resources to support you in any respect, and be pleasantly surprised when they do.
And it should go without saying, but do not enter into any kind of intimate relationship with any employees under your supervision, and in general, with the employees they interact with on a regular basis. This can go sideways in so many different ways that if you find yourself in this position you should just find a new job or otherwise remove yourself from the situation. And even in just casual social relationships, you should strive to be friendly but not friends, which can be awkward when you’ve been promoted from within and are already friends with some of the workers you are now supervising; in that case, you need to make it clear to all, but especially the friends, that they will not receive preferential treatment and that your expectations for performance are in accordance with role and experience regardless of outside social relationships.