The whole process consisted of an online application form, online aptitude tests and an assessment centre.
At the assessment centre there was a group exercise, a written exercise, a work-based competencies interview and a technical interview (which included a 10-minute presentation).
The group exercise was relaxed and not difficult - they're trying to see how well you work in a team, so remember to provide regular (useful) input, encourage quiet people to speak up, summarise regularly and try to keep to a time schedule for the task.
For the written exercise, I was given some information about a made-up company and had to identify some issues they were facing. It was obviously designed to be very difficult to do in the time given, so concentrate of being quick and accurate, and plan how much time you'll spend on each part at the start. Online verbal reasoning tests would be good practice.
The competencies interview was standard, full of "tell me about a time when..." questions.
For the presentation, make sure you stick to the brief given. Think of what interests you about the topic you choose to present and let that enthusiasm shine when you're talking about it. The technical interview that followed was pretty tough, so do go over the relevant parts of your degree. I was asked some questions relevant to my final-year project (including Fourier transforms, propagation of radio waves), some programming questions and some more general ones where I was expected to work logically towards an answer. Practice solving problems aloud and explaining your thought process - you don't need to know the answer, you just need sound logic.