It is important to ALWAYS read the question very carefully on IELTS writing task 2 to see exactly what you are being asked to do. There are many different essay types that require different ways to answer them.
Some of the types of IELTS essay:

• Agree – Disagree
• Advantages – Disadvantages
• Discuss two opinions
• Discuss both views
• Causes and solutions
• Causes and effects
• Problems and solutions

You may also get some of these tasks mixed up.
You should spend about 40 minutes on this task and write at least 250 words.
There are three things that you must have in your IELTS writing task 2 essay:

1. Introduction
2. Body Paragraphs
3. Conclusion

Some time out of the 40 minutes needs to be spent on planning. You need to be able to write the introduction very quickly so that you can start writing the body paragraphs. In the introduction, it is best to state the topic of the essay which you can paraphrase using the synonyms from the topic and the question given. After that, sets out what you will write in the essay. Some questions may ask for your opinion, some may not.
One controlling idea should be stated in each paragraph, followed by supporting sentences. The conclusion can be written in one or two sentences. Re-write the last sentence taken from the introduction and write it in different words. Answer and reason are the two things that should be included in the conclusion.