To stand out at an early stage like year 12, you only really need to go beyond surface level research as most applications will probably have. Let's taking Clifford Chance's ACCESS programme for example. Instead of having a quick glimpse at the firm website and saying something like, I want to take part in this programme because Clifford Chance is in a lot of different countries and I would like to work abroad in the future, you should do a bit more. Maybe try the firm's Ready, Set, Law Forage, and explain how completing this Forage got you interested in X aspect of the work being done at the firm, and how you want to learn more about how lawyers do Y.
Same goes for answering why commercial law. For this question, really avoid being general, firms hate when candidates are general with this question. Don't say I want to be a commercial lawyer because I want to work with big companies or because I like the intersection between business and law. Whilst those things may be true, that's not enough to justify your interest. Instead, you could again justify your interest with personal experiences. Like, as part of my school's Law Society we look at interesting matters and I was particularly curious to learn more about the Colin the Caterpillar IP dispute after the matter was brought up. This then led me to learning about commercial law more broadly, etc. Always qualify your interest.