Well, people do it differently, but I'd ask your dh and your dd what meals they like, add in your own favourites, and then you've got your plan.
You know then, what meals you are having for the next week, so buy the ingredients for those meals.
However
It doesn't work for me for the following reasons :
It's boring - same thing "because it is Tuesday"
It lacks spontaneity
It doesn't seem to take into account the fact that some days you will be late home from work, or need to go out early to a meeting or something
It must limit your palatte I'd have thought (?)
I like to go to the supermarket and see what is on offer (which saves money), and also see what the 'BBE' dates are. No good buying the chicken when you do your shop on a Sunday, because Thursday is your chicken day, if the chicken is BBE Tuesday, for example. I can respond to the weather too - I don't fancy a casserole when it is hot, or a salad when it is wet and rainy. Sometimes, if {again, just an example} the bigger pack of mince is much better value, then, if the dates work, I can think that we'll have cottage pie tomorrow and then spag bol in 4 days time, or whatever, because it makes sense with the ingredients that are there that week. Or I was thinking jacket potatoes, but they don't look that good that week, I can change my mind.
If I know a dc has been invited to friend's house, one night that week then we might choose to have the meal they don't like on that night.
I always buy fewer than 7 'meals' a week. We have one night where it is leftovers, or 'something on toast' or 'something out the freezer' etc., too.
There are lots of ways to save money if that is what you want to do, but, for me, meal planning isn't a help in that.