Just remember the basics: universities are given hundreds of applications with similar grades, so they’ll need your personal statement to see whether they actually want you as an individual.
First thing to do is to look directly into their websites and see if they offer any guidance on what they are looking for in prospective students. Make note of particular characteristics and include them, backing them up with specific activities you’ve done. Make sure to explain how your experiences relate to the specific course as well.
This won’t be a problem unless you’re applying to two or more courses, where it gets difficult to incorporate interests for all of them into a single personal statement. Try your best to balance them out by generalising statements so they fit to all of your courses. Be careful not to directly state any course names as the admissions team of another course may realise you are applying to several, which may suggest shallow interest in their course.
Don’t worry if you don’t have enough extracurriculars to impress them. Use your hobbies to show how you’ve dedicated your own time into the field. Read books or news articles in the relevant area, or do your own research. Be careful not to focus too much on the content though, and focus on your own thoughts and opinions instead. Also, sell what you’ve done for the IB! Mention your higher level choices and how they helped you develop insight into the area, as well as activities done for CAS which may be relevant.
Most importantly, keep your personal statement honest. Research a bit to figure out what everyone else is writing. Try to make yours unique so that it stands out and they remember you.
After all, you know you want to get in. All you need to do now is tell them why they will want you in.