Check that hot food is kept hot. Food in bain-maries should be steaming. Reheating lukewarm food is no guarantee of safety. In a restaurant it's not the plate that needs to be hot, it's the food served on it.
Check that cold food is kept cold. Chilled food should be stored below or behind the load line in open refrigerated cabinets in your supermarket. Never buy chilled food from a shop that stores it at room temperature.
When shopping, buy your cold food last and get it home fast.
Take an insulated bag with you to keep chilled and frozen food cold, especially if travelling more than 30 minutes to get home.