so meal plan either for the week or two.
make shopping list along side the meal plan.
look through the cupbourds at what you have in, you can easily make meals from what you already have in.
look through your freezer, you could probably eat out of there too.
have a "something on toast" night for tea
Buy bread on offer and put into the freezer.
try not to get drawn into offers unless you budget for them.
get a slow cooker or dust off the one you own. i make loads of cheepo meals in my slow cooker.
double cook and freeze half.
have frozen veg in freezer as well as fresh.
bulk up meals with this frozen stuff.
DO NOT buy ready meals, they are expensive, take up room in yourfreezer and can be made better and cheeper by you.
good luck, it takes effort but its worth the savings, honestly 
check out Marin Lewis website, its brilliant.