What should I focus on in my personal statement?

Your personal statement is all about conveying why you are a good candidate for what you're applying to, but this doesn't mean you should only be focusing on your academic achievements! Extra-curricular activities, personal hobbies, and even experiences that impressed you are all worth mentioning in your attempt to bring the following point across; "I am interested in this, and here's why". 

A well-rounded personal statement is the mark of an open minded individual, and universities tend to seek out students who exhibit not only a passion for their subject of choice, but for learning and challenging themselves in general. 

So while focusing on your academic interests and achievements is definitely essential, it's always a good idea to talk about other things that fascinate you in life, whether it be competing in your favourite sport or trying to make sense of the science behind Star Trek.