Hi I'm currently a second year at Cambridge studying MML (French and Spanish ex ab-initio).
I'd say for tips for applying - try and find a bit of a niche - for example if you put l'etranger on your ps just know that your interviewer has probably interviewed up to 20 people talking about that same book so maybe choose a different book, or a film. Don't be afraid to put something modern - Annie Ernaux, Delphine de Vigan these are all authors that'll prove that you are up to date with modern France and can be discussed and analysed just as thoroughly as you can analyse a classic French novel. Same applies for when you're talking about the language side of things if you go in talking about how much you love the different dialects of French from all over the world well they speak French in A LOT of countries. Pick one that you're interested in. What's the relationship between English and French in Quebec? How did Haitian Creole develop and is a creole a language in its own right or a dialect? Stuff like that that can provoke debate and that you can research really thoroughly.
In terms of applying for the ab initio language I know it's really hard to know what to write about but you can write about if you've ever visited the country before, or if you haven't why you'd like to. Any paintings, architecture, book, film you like about Germany? Maybe look up the texts that you'll study in first year for German and read something by one of those authors if you don't know where to start.
Any other questions I'm happy to answer