What I generally tell students is that your conclusion really should be brief. It should be about half as long as your introduction. It's perfectly legitimate to restate...rephrase your thesis statement in new words. Sometimes, if it's an ambitious paper, you might suggest some additional directions [and] additional insights, but you have to be cautious about introducing new material, particularly if the implication is somehow that you would have got to that if you'd had time. In that case, it's better if you leave it out. So, I'd say a brief restatement of the thesis and the key points [are] probably all you need.