As an AI language model, I can provide you with some tips and strategies to achieve a band score of 8.5 in IELTS writing. Here are some of them:

1. Understand the task requirements: Before you start writing, make sure you understand the task requirements and the type of essay you are expected to write. Read the instructions carefully and identify the key points that you need to address in your essay.

2. Plan your essay: Spend some time planning your essay before you start writing. This will help you organize your ideas and ensure that your essay has a clear structure. Make sure you have a clear introduction, body paragraphs, and conclusion.

3. Use a variety of sentence structures: To demonstrate your language proficiency, use a variety of sentence structures in your essay. This will show that you have a good command of grammar and syntax.

4. Use academic vocabulary: Use academic vocabulary in your essay to demonstrate your knowledge of the topic. Avoid using informal language or slang.

5. Provide examples and evidence: To support your arguments, provide examples and evidence from your own experience or from reliable sources. This will show that you have a good understanding of the topic and can apply it to real-life situations.

6. Check your work: Before submitting your essay, make sure you check it for grammar, spelling, and punctuation errors. Also, check that you have addressed all the key points in the task requirements.

7. Practice, practice, practice: The more you practice writing essays, the better you will become. Try to write essays on a variety of topics and get feedback from a teacher or tutor to help you improve your writing skills.

By following these tips and strategies, you can increase your chances of achieving a band score of 8.5 in IELTS writing. Good luck!