Essentially, you need to take a good look around your premises, weighing up everything that could potentially be hazardous. This could include stacking shelves, dealing with deliveries, the threat of violence? or electrical issues (even changing a lightbulb can? result in injury)?.
Your risk assessment will set out what steps you have already taken to minimise risk, what further action is necessary, who is responsible for that action and a deadline for it to happen.
Involve your staff as much as possible in the process, and identify their concerns. They may well understand the workings of the shop better than you. And make sure you review your risk assessment at least annually.