This piece for Malachain collects the advice that holds up in practice.
Cooking for a crowd is very different from cooking for a family. Large batches of food cool slowly, buffet dishes sit out for hours and fridges quickly run out of space. The main rules are to keep hot food hot, keep cold food cold and limit the time anything spends at room temperature to around two hours, or less on a hot day.
Plan the menu around what your kitchen can actually handle, and divide large quantities into shallow containers so they cool quickly. Use a food thermometer for meat and reheated dishes. Label dishes that contain common allergens such as nuts, milk or gluten so guests can choose safely. When in doubt about leftovers that have been out too long, throw them away.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.