In IELTS academic writing task 1, candidates are usually asked to describe some visual information. You may be given a graph, table, chart, or diagram, and you are asked to present the description in your own words. You may be asked to describe and explain data, describe the stages of a process, how something works or write about an object or event. You need to write 150 words in about 20 minutes.

To score high in this writing task, you need to focus on the following steps:

Think about the given graph, chart or visual image as well as the given information about it. Take note of the main trends and key features of the chart or diagram.
Start with an introduction: this is a description of what the given graph is all about.
Give an overview of the main trends noticeable in the given chart or diagram.
Give a detailed description of the noticeable key features in the chart, such as similarities, differences, etc.
For a detailed explanation of how to score high on this writing task, watch the following video lecture:
https://www.youtube.com/watch?v=mgn_GXq1N6s