Here's a tip:
when you make a sauce for lets say spaghetti portion it and freeze. Cook only the amount of pasta you want to eat with the portioned sauce. If you combine everything from the start and throw it in the microwave it won't taste very nice.
Salads: you can make a nice bowl of salad but don't put any kind of dressing on. Use what you want and the rest will stay nice and crispy in the fridge for a couple of days.
Make a stew, again portion it and eat it one day with rice and the other with boiled potato's, taste like a complete different meal.