...when cooking from scratch.
When you make up a batch of short crust pastry, make double or even treble the amount you need, and freeze the rest, ready for next time.
Grate a big block of cheese. Keep it in the fridge in a sealed bag ready to use, or freeze portions of it.
When you make pizza dough, make double, and freeze for another time.
Lots of meals start with fried onions. When you have a bit of time, chop up LOTS of onions, and cook them slooooowly in some oil, until they are rich and soft and flavoursome. These can be frozen in little bags, and will give a delicious flavour to many meals.
Use the slow cooker to make up a big batch of tomato sauce. Use this one night to have with pasta, the next to top some fish fillets, and use up the last bit on your frozen pizza bases, with your frozen, ready grated cheese for a super quick meal.
Cut chicken into strips, sprinkle with spices and seasoning, and freeze it in a bag along with sliced onions and peppers. Take a bag out before you leave for work, and you have chicken fajita fillings, ready to go, when you come home.
Crumble topping (flour, butter and sugar, rubbed into crumbs) freezes brilliantly, and hardly needs any time to defrost, so you can make up a huge batch when you have some time to spare, and freeze it in bags. When you want to use it, you can take it more or less straight out, crumble it over fruit with your finger tips, and bake.