1. The idea of a "draft" in IELTS doesn't really work. What you need to do is be as time efficient as possible and that means writing only once, not twice.
2. Start from a model or sample essay and use that as your plan. In truth, in IELTS you only need 2/3 different plans and these can be prepared beforehand.
3. The simplest plan possible is the "for and against" plan or the argument type essay. For this your 2 basic ideas are "Some people agree" "Others disagree" and then you need to think of a couple of reasons and examples for each point of view. Typically, reasons and examples are much easier to think of in the pressure of the exam than ideas.
4. Don't write too many words. You need to write at least 250 or you will be penalised, but you are wasting energy if you write much over 275 words. Try looking at some of my samples: these are all written with learners in mind: they're the sort of essays you could actually write yourself.
http://ilsielts.blogspot.com/2009/05/sample-ielts-essays.html.
5. Think about structural language. Language like "Firstly" doesn't do you much good, much better would be "The first argument in favour of this would be..". It is better language and it is 9/10 words long - you are that much closer to finishing your essay. Try looking here to see what I mean:
http://ilsielts.blogspot.com/2009/05/ielts-essays-coherence-between.html You will also improve your coherence by using this language and coherence counts for 25% of your marks.
6. Finally, and perhaps this is the really important point, don't start off by trying to write essays in 40 minutes: you probably won't learn anything much that way. Rather i suggest you start off by writing in an hour or so and each time you write you will write a little bit more quickly as your skills improve. In a fairly short while you will be writing in the 40 minutes needed. And, importantly, your writing will also improve.
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