I plan a week's worth of meals at a time, because it's the only way I can keep the grocery shopping time and cost within rational levels. I could probably get away with winging it more if I only cooked four or five meals a week, but since DH and I both work at home, and I cook lunch as well as dinner, it's more like 12 to 14 meals, plus any weekend breakfast cooking, plus any snacks or desserts, plus cooking homemade dog food. My planning is more organizational than nutritional, though -- other than trying not to serve more than one creamy/cheesy dish a day, I don't pay any attention to carbs, calories, fat, or whatever when I'm planning it out. It's enough trouble trying to figure out what vegetable dishes go best with with what meat dishes and how to creatively prepare that 957th head of cabbage!
Also, if I don't plan meals out, make a grocery list, and check the pantry, I am sure to forget the pine nuts, or the fines herbes, or the fish sauce, or some other arcane ingredient -- and since I like to cook and try to make a new recipe once a week or so, I'm always using arcane ingredients! Then I find myself running to the grocery store every day or so, and whatever I need is invariably located right next to the sugar free chocolate
.
A helpful tip: if you're just starting to plan menus, keep your old ones. After a month or two, go through and look at them, and you'll see a pattern emerge -- if you can make a list of four or five favorite meals, you've just cut your menu-planning time in half. I have a list of about 20 that I rotate through, for which I know the principal ingredients, the amount of leftovers, and the approximate cooking time. Now, instead of prowling through my recipe files looking for meals, I just pick the dishes off that list that best suit the needs of the week.