I know I've said this before. And your teachers will have said it too. But - read the question!
Why am I saying this again? Because I'm marking essays at the moment & I seem to be writing that phrase rather more often than I'd like. When I set a question, whether it's for a test, an exam, or an assignment, I always try to delimit it - to write it in a way that outlines what direction I'm expecting the student to take, or the sorts of things that I'd like them to consider in an answer. (You've seen the same in L3 & Schol papers.)
So it saddens me when people don't take that on board, & go off at a tangent or include stuff that might well be interesting but is also irrelevant to the question at hand. In other words, if asked for examples from New Zealand, don't tell me about cases from Africa or Australia. If asked to discuss applications of today's technology, don't talk about the possibilities of future, untried technologies. And so on.
Don't get me wrong - I love it when students come up with novel, insightful, perceptive answers, things that I might not have anticipated myself. That's great, & I encourage it. But that insight & perception still has to be applied to the question that was asked. (If enough students go off the beaten track in their answer, that would suggest to me that I'd set a bad question in the first place. But that's a separate issue.)