Improve your general listening skills
The goal of IELTS Listening section is to test your listening skills. Don't use practice tests to improve your score: it's not enough! They will help you to become familiar with the test, but won't much improve your listening abilities. It is much more effective to do various listening exercises, listen to general listening materials (radio reports, TV-shows, documental programs etc) and only after that do IELTS Listening practice tests.