The problem with "scenarios" is that (as evidenced here) there are often many ways to "skin a cat". Command is really about the demonstrated ability to make decisions. That ability doesn't mean a snap decision for every scenario you might face. The most important ability is the ability to manage. There are very few situations that require an immediate critical response. The most important things that you will need to manage are the resources available to you. Chief amongst these are time and space. Give yourself enough of both to suit the situation. Far too many people faced with an emergency or non normal situation rush to a solution. This often results in insufficient time or ground distance to execute a tidy conclusion to a problem. The other equally important resource is your crew. As part of your command management, you should properly bring them into your solution as quickly as time allows. Also don't forget all the other resources available to you, ATC, emergency services,operations and engineering. Communicate the situation as early as time permits and for all those resources, you will become the most important aircraft in the sky.
Becoming a commander will not make you a font of all knowledge, or provide immunity from bad decisions. However it will mean that somebody has judged you have good management abilities, and you should use that as the basis for ongoing improvement for the rest of your career. Inevitably you will make mistakes and continue to learn from them. Others should also be able to learn from you. Time critical decisions are normally recall items, or practiced simulator exercises, however any situation should be effectively managed by you, even as is often the case it means listening to, discussing with, and sanctioning decisions that are made by other members of your crew. Again within the bounds of what you assess to be reasonable, give people the space and time to come to their decisions as well. The only other advice I can give, is where possible (and it almost always is), always have a "plan B" or an escape route. Any decision made by or endorsed by you, belongs to you. As such you have the right to modify, change or abandon it as the situation warrants.
Enjoy your command.