I usually plan ahead for 3-4 days of the week, in advance of the weekly shopping. But the storecupboard and freezer have the basics of at least another fortnight of meals that I can throw together. So there might be chicken and pork and prawns and mince in freezer, jars of tomato and curry and chinese sauces, packets of dried sauces or casserole mixes, rice and pasta and spuds - all of which can make dinners quickly. Or use bits of those, with some fresh veg, herbs and spices, tins of tomatoes and coconut milk etc to make a similar dinner but cheaper and (usually) tastier and better for you - if time allows.
It means sitting down once to consider what kind of meals your family likes - make a list of 15-30 if you can, of all types (fast, slow, casserole, roast, conveneince in oven, simple snack to full blown gastronomy!!). What is your daily/weekly/monthly schedule like - are there times when you have loads of time, or are you always busy needing meals in a hurry. Having a plan for meals that need a fair amount of prep/cooking time, and other meals that can be made in a hurry for no energy/no time nights. Consider meals that can be made in advance and reheated (lasagne, spag bol sauce, curries, stews). Can you set your oven to turn itself on and cook while you're out? (Absolutely great to have!!). Can you make meals with leftovers (even just leftover roast chick in a sauce with rice/pasta say)? Are your family fussy in any way (veg, meats, spices, glueten-free, diabetic, .....) that you need to watch?
Once you have the basic list of a nice range of meals that you know everyone will eat, start to put together a store cupboard and freezer and fridge things (like cheese, eggs, butter, sour cream?), based on having a few backups for these - the basic ingredients and things that can do lots of different meals. Build that up over time.
And once the basics are sorted, start using your list of recipe. Make sure you give enough variety, and check the week ahead in planning the weekly menu (like - is there sports training for DCs one night meaning eating at seperate times, or "fussy Dhousehold person X is not in Wed so we can have ABC" (or the opposite - fussy person being IN means you have to provide DEF), or "I have to work late on Tues, so it will have to be something quick or prepped in advance"). If you have a chance, look at specials etc beforehand, but start with getting the idea sorted first.
And you WILL save money over time. It may not seem it starting off when getting the storecupboards etc sorted, but when you have all those extra little bits already in, it really does save money, time and effort.