After your application is complete you may be selected for a telephone interview. This was straightforward and based on competencies (can you tell me a time that...?) and an understanding of the energy sector. They send you details of the competencies before the interview and the assessment centre which is very helpful and these are a great place to start preparing. The assessment centre contained another interview fairly similar but more flexible around a few key areas (again, refer to the competencies they list on your invite). They'll also want to hear what you know about the future of the sector you are applying to. By far the most useful part however is talking to the assessors over lunch, as you get to hear what they do and show what your interests are. There is also a presentation you have to prepare on the day itself (my advice would be to keep an eye on your preparation time) as well as a group task. The group tasks involves everyone and is nothing to worry about, nor something you could particularity prepare for - just make sure you communicate well with others and try and keep the discussion structured and moving forward. My main advice is prepare examples of you displaying competencies in the past, relax and talk to the assessors as much as possible about what they do, what you find interesting, etc.