Hi iddqd,
I would have the same problem you have, being left without any direction at all like that. On the other hand, if instructions would be very complex and precise, I'd have trouble too, because there'd be nothing left that I could do my way. Maybe you can explain to the teacher that you need at least some direction, e.g. he could give you an image of a "celebrity" from a magazine that you should include in your drawing, or he could tell you to draw purely abstract, avoid anything figurative, and express your notion of "fame and celebrities" with shapes and colors.
I'm sure the people in your class were genuine when they told you they liked the drawing you had made. I did a drawing class too, and the drawings I got the most positive comments on were not the ones I thought were best. I liked the drawings I made where the things I drew looked most 3-dimensionally real (like "coming out of the paper), while others liked the ones they found most "expressive". NT's apparently like it when you exaggerate stuff, e.g. make dark parts pitch black, draw thick lines where subtle edges are, make bright parts really shiny, etc., so that you can see what it is from a mile away, poster-like.
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There is nothing that is uniquely and invariably human.