Make complex vocabulary, as much as practical and; try to start each sentence with a complex word and make the first word of the task as complex as possible.

Practise + practise again - make writing in English and answering IELTS questions as automatic as possible.

Understand the different requirements of the exam, such as 150 words minimum etc..

Make sure that you fully answer the questions.

Many people may write by hand only a little - try to redevelop this skill.

Make synonyms and try to avoid repeating their vocabulary.

Make a schedule and watch the time to have enough for  checking etc..

Careful of your spelling and grammar - get it checked by a native-level teacher etc..

Make sure that the response is clearly structured.

The IELTS exam can be a "high-energy" task - try to have enough food nourishment so that you can easily do the tasks.