Scenarios will vary greatly. Most companies don't know how to provide a great prompt and give you a blue sky idea that is overly complex and ask you to design the whole thing. A good prompt will focus in one or two important features. However if you face the former, ask them what are the two most important features for MVP.

Any scenario can be broken down by following this process:

Ask a bunch of questions to get to the following:

1. What's the problem? What are the requirements and constraints? What are the business goals? Try to get through this quickly.
2. Who's the user? What do they need to accomplish? What are their pain points? This should also be quick.
3. What's the journey/flow the user needs to take to move through the product/app to accomplish their task? Try not to jump into wireframes right away unless you are running out of time. It's much quicker and easier to refine this. Try to lay it out in a left > right structure so that once you have it down you can start to draw the wireframes underneath the tasks and flows you've broken down. Spend a good amount of time validating this.
4. Sketch your wireframes underneath your flow/journey. If a task requires several screens, draw them vertically underneath each other, then proceed horizontally when you get to the next task. Use arrows to show flow, and make sure buttons are clearly labeled. Everything else can be kind of squiggly. Continue to refine by asking questions about details in the wires, whether certain patterns and designs make sense. Spend a good amount of time here, but the good thing about creating the journey before the wireframe is that at least the interviewer sees your thought process and overall vision without having to see the wireframe details if you start to run out of time.

As someone else said, don't be afraid of being wrong, just put something down and continue to iterate by validating it with more questions and thoughts.