Because of the risks in catering for a large group, you need to be even more careful than usual about preparing food to prevent any bacteria being introduced by cross contamination.
Wash your hands before you start preparing and between preparing raw and ready to eat foods – learn about Handwashing. Wash chopping boards, knives and anything else which will come into contact with the food between preparing raw and ready to eat foods.

Cook poultry, minced meats, sausages, tenderised meats and other pre-prepared meats until they reach 75°C in the centre using a meat thermometer. No pink should be visible. Steaks, chops and whole pieces of meat should be cooked to 63 °C (medium rare) using a meat thermometer and left to stand for 3 minutes to kill any bacteria and parasites such as Toxoplasma gonddii. As a guide: well done is 77°C, medium 71°C and medium rare 63 °C (leave to rest for 3 minutes).

Do not allow cooked meals to cool on the bench. As soon as steam stops rising, refrigerate or freeze in a leak-proof container.
Don’t prepare food if you have vomiting or diarrhoea (gastroenteritis) – you’ll be sure to pass it on to your family and friends.
Don’t leave perishable nibbles, like dips and soft cheeses, out in the temperature danger zone for too long. It is better to divide them into small amounts and replenish with fresh portions as required. This also makes them look more appetising. Don’t mix fresh top-ups with ones that have been outside for some time. Low risk foods, such nuts, crisps, crackers, etc. can be topped up every hour or so.