On Writing Task 1 your piece will be marked lower if:
- It copies material straight from the page.
- It ignores the visual components of the text.
- It sounds boring and ticking-the-boxes.
- It races through the material in the hope of covering everything.
- It has no sensible paragraph organisation, with topic sentences and some logic or 'approach' tying the whole piece together.
- It only *describes* the information, and makes no effort to explain it or talk about its importance or meaning.
Other than that, you can choose whatever form works best for you: standard essay, speech, creative etc. Pretend the A3 is your research, and you're writing an essay (or whatever) on the topic - would you just copy your research out, point by point?
On Writing Task 2 you will score lower if:
- You have no clear point-of-view or argument.
- You contradict yourself and swap between points-of-view.
- You only have one argument and essentially repeat the same point over and over with slightly different words.
- You don't develop you argument in different ways and depths and instead just reiterate your first argument in subsequent paragraphs (see what I did there? haha).
- You basically just copy the prompts you're given.
Other than that, feel free (like above) to choose whatever writing form you like. Just decide on an argument, and then discuss it, giving reasons.
Think of the GAT as being the safety net you don't know you need until after it's too late to do anything about it

Don't stress, but do give it your best shot.