Oxford Tutors are looking for three key points when it comes to the TSA:
1. A clear argument
2. A clear structure
3. The ability to think outside the box
The first two points are particularly important. Prospective applicants (and the teachers at my secondary school) tend to overemphasise the final point. While creative thinking is useful, tutors have explicitly told me that they are looking for the ability to persuade and to structure an argument. The first year of Oxford, for the social sciences and the humanities, is largely focused around improving these skills. Demonstrating them will give you a significant advantage!