While there are different types of essays, in general use your introduction to look at the topic and indicate some of the issues it raises or you will be discussing in the essay. Your opinions or conclusions should follow after you have discussed all the issues and looked at the evidence in the main body of the essay. Hopefully your discussion will have led to the readers' acceptance of your conclusions.

Remember that not all IELTS essays require your opinion at all. But in an essay that does you really have two choices. A. a discussion of both point of view followed by a conclusion based on the strength of the arguments for each (as Warren suggests). B. a clear statement of your opinion in the beginning followed by arguments which support this. The examiner has no preference, as long as you are logical and consistent.