A personal statement is exactly that - personal. It should include why you as a student are applying to study for the subject you've chosen, and what makes you the best fit for your course choice. Your statement should also reflect what you hope to gain from the course/any specific modules that you've researched are on it . Extra curricular activities should be included too but I would strongly suggest linking them back to the subject you are applying for - you want to present yourself as someone who has a clear passion for your course.