The conclusion paragraph for both of your issue and argument GRE essays should be a strong, clear statement of your purpose. It should include reference to the information that led up to it throughout the rest of the essay and should leave your reader without any doubts about your message. As with the other paragraphs, it is best not to start this one with "In conclusion ...". The conclusion should summarize everything you have said and make your main point clear but it should not revert to generalizations. For example, consider the following:

The day my friend went drinking and driving I learned a lot about life. I realized that what I did was wrong and dangerous. Ever since that day I realized that I should be more responsible in life and that drinking and driving is always wrong.

This conclusion is full of generalizations. It does not reiterate any articulated message about the essay itself or speak specifically to the significance of the example that the author has used throughout the text.

A better conclusion paragraph is the following:

That day was one of the most important in my life. I realized that day that what I understood about responsibility was naive at best. I understand now that being responsible means thinking about the possible consequences of my actions before I make my decisions.

This partial conclusion covers more specifically the message intended by the author. It reminds the reader that the evidence used throughout the text is significant to the author’s purpose and main point. Also, the better conclusion paragraph not only conveys a personal message, but it relates that point to a more insightful, broader message. You'll definitely want to do that when you write your GRE essays. Don't just say that such and such points are important to you. Rather, why are they important? Do they help explain an idea or problem that is experiences by many people? Do the points that you raise allude to a broader issue, one that is experienced by people of different nationalities?

Once you have an idea of your conclusion ready, review your essay’s introduction to be sure you have stayed on track throughout the essay. For the GRE issue essay, you'll want to make sure that in the conclusion paragraph you reiterate or at least allude to the claims that you foreshadowed in your introduction. And, for the GRE argument essay, in the conclusion paragraph you'll want to be sure that you unequivocally take a strong stance and decisively say whether the provided argument is good or bad. By that time, in your body paragraphs of your GRE argument essay, you should have alluded to enough details to make your stance convincing.

A common mistake is to write an essay from the beginning to the end and to drift slowly away from the intended purpose throughout the body paragraphs. An easy check for this is to compare the introduction to the conclusion and be sure the ideas are similar.