Waitrose assessment days have a selection of different tasks. There are a number of exercises to do and also food and refreshments provided. It is likely that there will be a group exercise, maths and verbal tests and an interview to check for competency as well as a presentation.
The day will probably start with a presentation about Waitrose and what they are looking or in their employees. There are then activities that you have to take part in. Previous attendees are asked not to tell people what these involved and so no one really knows. However, by looking at what is expected in group exercises in general, such as showing leadership skills, team skills etc then you will get an idea of what to do. It is important to get to know the other candidates as it will show your team working abilities. You may also be working with them if there is more than one job on offer and so it will put you in good stead for that.
It is also wise to prepare for the maths and verbal tests. Although specific details of these are not available, looking at general tests that they may be similar to, can really help. This will not only improve your skills but also make sure that you have confidence in your abilities.
Preparing for the interview stage will be like preparing for any other interview. Make sure that you know a lot about Waitrose and the role that you are applying or. Also make sure that you have some questions prepared to ask them. You may want to ask some questions throughout the day, to demonstrate how keen you are, but make sure that you save some for the interview as well.