Improving score from 6 to 7 is important for candidates who are willing to find permanent residence abroad. Scoring band score 7 in IELTS is tricky as it takes a lot of hard work and dedication. Moreover, you need to understand where you're losing marks. It is, in fact, crucial to tackle this particular problem first before you re-appear for the ILETS. You need to check whether it is writing section or not first; it is because of the fact that many test-takers struggle to achieve their desired band score due to less scoring in the writing section. 

If you lack behind in the writing section, then here are some points that need to be considered. When you're given a topic to cover, then you'll have to answer or write about it in a very diplomatic manner. It is advisable not to take sides when you're writing for that particular topic. However, if you are asked to give your opinion on a specific topic, then it is advisable to write about your thoughts and views.

Before you start writing, make sure you take out first few seconds to jot down your points on what you're going to write about. This is going to give a proper direction to your thought process. The most important is your spellings and make sure you don't mess up the tenses and make any grammatical errors.

Make sure there is a flow in your wiring. Moreover, DO NOT deviate from the topic that is given to you.

The writing section is only for 45 minutes, and you have to cover 250 words in this duration. If you're smart in managing things, then you'll have time to give a beautiful introduction and a conclusion. A good introduction and conclusion will set the tone for the reader, and it will prevent you from deviating from the topic.

Hope this helps!