Vegetables should always be covered with liquid and placed on the bottom of the slow cooker. Meat should ideally have liquid that comes at least halfway up the sides to ensure even cooking. Depending on the size of your slow cooker you may need to add extra stock and reduce it afterwards, if you are cooking a small piece in a large cooker, for example. However, the liquid should not be more than a few centimetres from the top in case of spillage.