Which part is more difficult? As you've mentioned, that totally depends on the student because every student will have their own stronger and weaker skills. 

How to get a higher band score? - GET TO KNOW THE EXAM! I cannot stress enough how important it is to know what's expected of you. You can and you should use different websites for this, as was suggested by Kieran earlier. The information is plentiful and readily available but, unfortunately,  it's easy to get lost in it so here are some tips on what you should primarily focus on:  

LISTENING and READING: there are 6 main question types for each of these skills and you need to know how to deal with every question type. I'd recommend to read about them on the official IELTS website first and then search the Internet for a specific strategy you'd need to use for every question type.

SPEAKING and WRITING: study the band descriptors!  You'll find them here: 

Speaking: https://takeielts.britishcouncil.org/sites/default/files/IELTS_Speaking_band_descriptors.pdf

Writing task 1: https://takeielts.britishcouncil.org/sites/default/files/IELTS_task_1_Writing_band_descriptors.pdf

Writing task 2: https://takeielts.britishcouncil.org/sites/default/files/IELTS_task_1_Writing_band_descriptors.pdf 

The band descriptors are your guide to what the examiners will be assessing and what you need to show in the exam language-wise to achieve a specific band score. 

Hope this helps and good luck with your exam)).

If at any point your test preparation gets too overwhelming, you can book a lesson with me and I'll be happy to answer your questions or help you with practice) 

Hi Sam, to find out about the format of the test, visit the official IELTS page (https://www.ielts.org/about-the-test/test-format). Here you will also find some sample questions under the "about the test" tab.

You can also find some free test questions and preparation materials at the British Council website (http://takeielts.britishcouncil.org/prepare-test/british-council-online-resources). These are a good place to start if you know nothing about the test.

There are also some great websites online with IELTS tips and strategies, for example: https://www.ieltsadvantage.com/

These will help A LOT but you may eventually need a teacher who can assess your speaking and writing tests and work with you to improve the areas that are lowering your score.

I'm a professional English teacher that specializes in IELTS preparation, and I would be happy to help you prepare for the test. Take a look at my teaching profile and send me a message or request a trial session if you'd like to come up with a study plan.

Take care!

Kieran