The French call it "mise en place." Everything in it's place....meaning that your prep work is the key. I agree with kitchenelf, if I am making dinner one night and require an onion, I dice double the amount and put the other diced onion in the fridge for the next night's meal.
While I don't freeze whole meals, I find that marinara sauce or bolognese sauce does freeze particularly well. so I make a large batch and freeze individual portion sizes in ziploc bags for future use. Then I can just boil the pasta for a quick meal!
Also,some dishes can do double duty in another meal later on. Leftover sauted spinach for example, ends up in a spinach and bacon quiche and topped with some caramelized onions(that I already have diced on the fridge!)
Hope this gives you some ideas.