You were promoted because you were good at the job. Now the job is different. The first 90 days set the tone for everything that follows, and most new managers spend them doing the wrong things quickly instead of the right things in order. Here is the order.
Month One: Listen Before You Lead
Your instinct will be to prove yourself by changing things. Resist it. In the first month, your job is to understand the team you have, not the team you wish you had. Sit down with every person one to one. Ask what they are working on, what gets in their way, and what they would change if they could. Take notes. Do not promise fixes yet. You are building the map you will need for every decision that comes later. The free 30-Day Email Course walks through this week by week, with one practical task per weekday.
Month Two: Set the Standard
Once you understand the team, decide what good looks like and say it out loud. Standards that live only in your head are not standards, they are disappointments waiting to happen. Be specific about what you expect, by when, and why it matters. This is also when you start modeling the behavior you want to see, because people watch what you tolerate far more closely than what you say.
Month Three: Hold It
This is where most new managers fall down. Setting a standard is easy. Holding it, especially with someone you used to sit beside, is hard. But a standard you do not hold is worse than no standard at all, because the team learns that your word does not carry weight. Hold it consistently, fairly, and without drama. If a hard conversation is coming and you are dreading it, that is normal, and it is exactly what the Hard Conversations resources are built for.
Ninety days will not make you a finished manager. They will make you a credible one. That is enough to build on.