A good reference and some basic retail qualifications will go a long way. Show that you are passionate about detail and people and just be yourself - do not be shy to brag a bit on your abilities. They want to see if you have leadership and can take pressure and all the tests are also directed to be pushing you against time. Make sure you study the given materials and come prepared when you need to write a test - they provide a basic numaracy test working on percentages mostly, so warm up on maths (not rocket science though). Have a look at their website and beliefs and always keep them in mind during the interview process.

The interview process was fairly easy. They asked basic questions and I was only a one round recruitment process. The consisted of a panel who were friendly. But do make sure you prepare.