Before imparting a lesson assessment it is imperative to prepare something, not just "wing it". Here are a few thoughts on how to do this.

Build the assessment and work trough it. Time it. Make sure it is possible to complete in the allotted time.

Check in on progress often. Any doubts should be answered as soon as possible, to minimize the amount of absorption time. Specially at the beginning, often times starting is the most difficult part.

Feedback, feedback, feedback. When checking in, be prepared to give feedback, affirmative or corrective.

Avoid intimidation. A blank project is incredibly frustrating. Have notes, links, videos, starting suggestions available. As the mentees become more knowledgeable and experienced a blanker project can be imparted.

Preparation. Another way to mitigate theblank slate is to make preparation part of the assessment. Have them make a list/folder of helpful tools/procedures/previous projects, that might come in handy.

Clash of ideas. When the mentor's ideas clash with the mentee, have the mentee share the thought process, allowed them to practice those persuasive skills.You are mentoring an individual not a mindless drone.