Your first boss might teach you how to be a good boss, or exactly what not to do. Both lessons are worth keeping.

Either version hands you a working model, which is more than any advice manages. A good one shows that being fair and effective at once is possible, and a bad one gives you something more precise: a specification of what not to do, learned from the receiving end, where the cost is obvious. You are being taught either way. The lesson simply comes in a different flavour.

So decide now what you would want somebody to say about you if you ever end up running anything. One sentence, written down while the memory of being managed is still fresh. It will be more accurate now than in twenty years.