I applied to girton. I worked on some mechanics problems and then general engineering knowledge in the technical sense. One of my teachers at my school was actually an engineering admissions tutor and said if you get easier questions its most likely that they are just interviewing you for the sake of it. Thankfully i managed to squeeze in around 5 practice interview sessions and so i managed to get any bad parts of my technique out but I would say that its all about practice. There isnt much you can do to prepare except for read your ps and tighten up on any general questiosn you may get on that.