I did QET last year, from what I know, you'll be doing some grammar editing and writing of an argumentative essay. For your essay do CLEARLY write out an outline, from what I know, they actually do look at your outline and give you marks for organization. Just remember to follow proper essay structures, keep arguments precise and conclusive, don't beat about the bush etc. Plan out the essay before writing.
My written english isn't that good, and I almost made it pass the mark(1 band below the passing band?). Ended up having to take EG1413, its nothing too hard though ,just a waste of time. If you bother to go for classes and do their assignments, you can't fail that module, though its just a waste of time.