What should i focus my personal statement on if I am applying for a medical/dentistry school

The medical school wants to know whether you will be able to handle the intensive course that you would be studying. So whilst it's good to display your passion for practicing medicine and conveying how much it means to you, focus primarily on displaying your passion for your subjects. Pick out subject areas that you have covered in your A-level subjects which you can apply to medicine, for example if you have studied statistics in maths, comment on how that will help you when you study epidemiology in medicine.
Specifically naming topic areas in medicine that you are excited for - as well as linking them to topics you have already studied in A level, means the admissions officer will be more likely to accept you over someone who has only listed his work experience and passion for practicing medicine. This is because the admissions officer will be more confident that you are able to withstand the tough course which lasts 5/6 years which is extremely important to the university as they don't want to invest into someone who will drop out in the future as they cant handle the course.