At any level, the conclusion to an English essay should not be merely a bland summary of the content already explored. It may be a good idea to summarise the main points that have led to the final discussion-point, but the concluding paragraphs to an essay should be seen as primarily the culmination: the most interesting and important idea that all prior content has built towards.
In this respect:
- Mention the main points of the essay as it has led so far...
- Then integrate this with this final discussion-point, exploring this with textual evidence as in the "body" of the essay
- The conclusion should not raise a number of unexplored points, but you can stand out if this final point develops a new question, idea or intertextual link (such as a quote from another book). Leave the reader or marker with the sense that your line of argument has fulfilled and goes beyond the basic needs of the question or mark scheme: it has the potential to go even further, perhaps by reading the question in a new light.
Conclusions are the single most difficult aspect of an essay. It should be tight, have momentum, and feel like it wraps everything up in the process. (Just as with my tips for introductions, these are my experiences, and are by no means fixed rules to follow). However, with some very easy things to avoid, they can take no time to write, and yet have the most influence on the essay.
Save something new to say for the conclusion. For me this has always been a must, and conclusions which recap the essay have always been suffocated by red pen. The conclusion is a chance for you to reveal your own opinion and perspective without saying "I think". I often favour starting conclusions with 'Perhaps' and then go on to offer something slightly new to my argument. The one thing to avoid is being controversial for controversy's sake so that you don't raise more questions than provide answers. Something like "Perhaps Gatsby is neither protagonist nor antagonist and is therefore not just a reflection of the world around him but shines a light on something within the reader themselves" with a bit of explanation can really have a large impact on the reader.
Try not to let the conclusion come out of nowhere. Certainly finish your final line of enquiry and make sure that if you didn't have time to write that conclusion you will have said all (but one) of the points you have to say.
Teachers have varying opinions on conclusion length, but realistically if it isn't two lines long or 1-2 pages, then it's absolutely fine. If you have something to say, say it!
Write a little bit passionately. Of course not over the top, but try to enjoy (or force yourself to enjoy) writing something that comes from you and is fresh and new. Just as in the introduction, your teacher will thank you.
Conclusions are hard because it is the part that sticks in the teacher's mind when they give you the marks - but this can work to your advantage. Be a bit fiery and try something new, and it almost doesn't matter what you wrote before!