For the writing section, one way to brush up your writing skills is to write more essays. You should write as many DIFFERENT types of essays as you can, so that you would be armed with more ideas for a variety of topics in your head before you turn up to the IELTS test.
For example, you might want to write essays that are related to Economics, Law, Physics, Education, Sociology, Politics, Management, and so forth. The following list, which is by no means exhaustive, shows possible essay titles that you might wish to use:
Law: Many people around the world are not in favor of abortion. Discuss, with reasons, whether or not the government should introduce a law prohibiting abortion.
Physics: Isaac Newton discovered gravity. Discuss the ways that the work of Isaac Newton on the discovery of gravity has contributed to our society.
Education: It is argued that parents should send their children to boarding schools so that young children can learn to live independently. Do you agree? Support your arguments with reasons.
Sociology: The society has different expectations on men and women. For example, men should be strong and brave and women should be caring and conscientious. What personal characteristics and social values do you think the “perfect male model” and the “perfect female model” should have?
Politics: “A right-winged government that supports free market philosophies is better than a left-winged government that favors socialist policies.” Do you agree?
Management: How should a company’s managing director manage its employees? Discuss various methods that a managing director can employ to manage the company’s staff.
It is also important that you try to write your essays NOT by typing them out on a computer, but by writing them on pieces of paper with a pencil or a pen. You should know that in the IELTS test you must write your essays manually by hand so it is important that you get used to the format of the real IELTS test. Furthermore, after you have done your essays, make sure you give them to a native English speaker to mark them so that he or she can give you advice on how to improve your English.
In order to increase your range of vocabulary, you can try taking a piece of paper and making a list of the words that you are not familiar with or that are unusual, and then writing the corresponding definitions next to each word. Make sure you learn the spelling of those words and their meanings regularly.
You should also try to communicate (be it speaking, listening or writing) as much as possible in English in your everyday life. Try thinking in the English language as well. In that way, you would be able to build up your confidence before the IELTS test.