When you are cooking a large meal with lots of different parts to it you need to make sure everything is ready to be served at the same time.  For example with a roast dinner, the meat, potatoes, vegetables, stuffing and gravy all need cooking for different lengths. 

A great tip is to work backwards from the time you want to cook and write down the lengths that the individual dishes need cooking for.  So if you want to eat at 2pm and the meat takes 90 minutes to cook it needs putting in the oven around 12.15pm, to allow time for carving.  Plan in advance by creating a schedule of when everything needs putting on to cook and follow it.