I have achieved an IELTS band score of 8.5, and in the Writing section, I achieved eight bands. Following are some of my quick tips and guidelines to be developed when writing an IELTS essay, and it is applicable for both IELTS - General and IELTS - Academic. Here it goes:
1. Organise your article into 4-5 paragraphs. The first para will be the introduction, the last one will be the conclusion, and then you should have 2-3 body paragraphs. Each of these body paragraphs should contain a separate idea. As an example, let's say the essay topic is "Shopping malls are replacing small local shops in cities and towns. Do you think it is a positive development? How can local shops sustain and co-exist with the shopping malls ?" You give an introduction in the first para, the second para about positives of shopping malls, third para about some negatives of shopping malls, fouth para to answer the second prompt about how small shops can sustain, last para to give a conclusion. The structure remains same, but this is just one way, you don't necessarily have to provide both positive and negative (in agree/disagree type essays), sometimes you might want to talk about one side only.
2. Make sure you re-read the essay question description and answer all prompts. The example in point 1 above has two prompts, so make sure you cover both.
3. Your essay should be of minimum 400 words. It can be more than 400 words, but it should not be less than 400 words. What I suggest is that when you practice, take a print-out of IELTS official mock test or sample paper answer sheet (it is readily available over the internet) and write your essays on these sheets rather than your notebook or register. This way, you will know how much of the layer it takes for your writing to cross 400 words. You are not going to count words on the test day. It is a very crucial tip because by following the word limit, you can quickly score marks for correct word length.
4. I have written essays for both IELTS as well as PTE and scored 8/8+ in both (79+ is PTE equivalent of IELTS 8+). For someone who has done both IELTS and PTE, I can tell you get enough time in IELTS to write an excellent essay (in PTE, it is 200-300 words in 20 mins). In IELTS, it is 400 words + in 40 min. So, for IELTS, take 4-5 minutes to think and (write in very brief rough notes on question paper) how you are going to organise your essay. Don't start writing immediately. Take these 4-5 minutes to be clear on how you are going to proceed with your article and have your thought ready. Then begin writing. If your ideas are bright, you would be able to finish writing the whole essay in 30-35 min. I would recommend you complete this before 35 mins so that you have last 5 mins to revise and check the spelling mistakes.
5. It is an obvious one - write-in clear handwriting which is understandable. It does not have to be necessarily beautiful, but it should be understandable if you know what I mean.
6. Another obvious one - make sure your grammar is correct and use punctuation correctly.
The above six tips are the ones which can be quickly followed by anyone (even someone with less than average or average core English) and can get you 7 or 7.5 in writing. There are some other tips to be followed to enhance your score further to an 8 or 8.5 which I will list below, but these may require better English language core skills.
7. Use collocations and useful vocabulary. Will explain about collocations later.
8. Try not to repeat the same word, unless it is a noun. Use synonyms instead.
Maybe a few more, but these are the ones I can think right now, and I think this can fetch you an 8 or 8+, even if your content is not very in-depth or comprehensive (of course it has to be true to the essay topic and bring in some key ideas).
If you need more help with IELTS writing tasks, leave a comment below.