The key thing to remember when approaching extract questions is to stay calm! It is easy to panic when faced with a question like this - as long as you know your text well and have practised sufficiently, you are going to be fine!
To begin, read the extract in front of you carefully and take time to think about it on its own before moving on to the question. Once you have done this, read the question and highlight any key words relating to specific characters, themes or mood, as this will help remind you where to focus your essay as you write.
Having done so, re-read the extract with these key ideas in mind. Try and highlight quotations that you believe are relevant to these ideas. At this point you should also be looking out for any literary devices (such as metaphors, hyperbole or alliteration) that the author is using.
In terms of essay structure, I would suggest using a 'PQE' method, so that each paragraph contains a clear point (Steinbeck presents Curley as an aggressive character), a quotation to support this ("his hands closed into fists"), and an explanation, which should expand on your point and highlight any literary techniques being used (adverb 'coldly'). An A/A* answer may also link this point to a further example. For instance, I may use George's reaction to Curley as further evidence of his threatening nature ("George was tense and motionless").
It is important that while writing your answer you are consistently referring back to the focus of the question - the key words/ideas that you highlighted initially. You may want to refer back to these at the end of every paragraph to make sure that your point is relevant to the question being asked - when writing an essay it can be easy to lose focus and this will significantly reduce your score.