It's a good idea to do practice tests (e.g. using the Cambridge IELTS books) in preparation for the listening exam. Here's some advice to help you benefit from doing practice tests:
1. Your score is not the most important thing
The important thing is what you have learnt by doing the test. Were there any new words or phrases that you can learn? What did you find difficult? Did any of the questions trick you? In other words, what do you need to do to improve your score?
2. Check how accurate your answers are
Be strict with yourself; every grammar or spelling mistake is important. For example, if the speaker says "The library has a collection of newspapers", you must not write "collection of newspaper".
3. Get into the habit of moving on
If you missed something, forget about it and move on. Always prepare for the next question rather than worrying about a previous question. When you are given 30 seconds to check your answers, use the time to look at the next section instead.