You should know what John Lewis expects of its service to people and what their tag line is;
“John Lewis - Never Knowingly Under Sold”
Get exact examples ready to use. For example, when have you worked as a team? Not just simply, I am part of a sports team, but they are wanting specific examples.
Brush up on background knowledge about the company. read about company ethos.
Learn how to find what a customer wants and sell them the most appropriate thing. Asks lots of questions.
Have lots to talk about with regards to yourself and your personal achievements, talk about skills you have which are relevant to the supermarket assistant job, talk a lot and take control within the group interview
Read the details on the job application hub about what is expected of partners. The partnership behaviours are openly displayed online and you need to ensure that you meet them.
Make sure you participate in the interview - it's an instant "no" if you don't talk during a group interview!
Be confident and research information also be yourself and reflect on the fact of being a people person with great customer service skills
Be very well prepared & presented
Be yourself because you won't be able to maintain a front. They are looking for team players.