Good luck with your interview! As we're sure you know, KCL Medicine interviews are in the MMI format.
In order to prepare for this style of interview, an important thing to start doing is to practice forming answers to mock questions under short time-frames. You may only have a minute before each MMI station to prepare your answers!
Different stations tend to focus on different aspects, so be sure to do a little research - perhaps Google search interview questions based around the following:
-You could be presented with a set of instructions that describe a situation involving an ethical scenario, which you will then be asked to discuss or try and solve.
-You could be given a scenario involving an actor - for example, you might have to break some bad news to them or gather specific information.
-You may be given a task involving teamwork with other applicants.
-There might be a station where you are asked a traditional interview question or given a reading comprehension exercise. So don't forget to practice the more traditional style questions like "biggest problems facing the NHS", "why you want to study Medicine" and "why you chose KCL" etc.
-You could be given a sheet of data and asked to provide analysis of it - so be sure to be up-to-date on your science/maths syllabuses, and do some practice data-interpretation of graphs! Perhaps ask your biology teachers for some mocks!
There could also be stations on other topics, so don't just focus on the topics listed above.
Also, Google search 'Richard Lehman's Weekly Review'. Dr Lehman is a retired GP who writes funny reviews of the latest and most interesting medical journals/papers (you can check them out here).
We've also got a free blog here covering some general top tips for MMI preparation!