I plan out suppers for Sunday to Saturday, and typically grocery shop on Sunday to pick up most of what I'll need (exceptions being things like fresh fish, which I like to buy the day of). I also make sure we have a selection of things to choose for breakfasts and lunches, and plan those particular meals around what I'm planning for supper (for example, if I have a more points-heavy meal planned for supper, I go lighter in the day). It's just something you have to get used to doing and then after awhile, it becomes second nature.
And if you bite it, write it.