Rather than approach meals on an ad-hoc basis, consider this: If you take the hurry and unpredictability out of meal preparation, you'll be rewarded with a much more wholesome, nutritious and flavorful meal.
Start by streamlining your shopping to just one or two days each week: Fewer trips to the store mean fewer opportunities to buy more than you need, or the wrong types of foods. Try to shop on the weekend or whenever you aren't rushed for time (or hungry for dinner). You'll be more inclined to focus on what you are buying, and pay closer attention to nutritional information on the labels.
Whenever possible, shop at farmers' markets and greenmarkets, or sign up for your local Community Supported Agriculture (CSA) plan. You'll get the freshest seasonal produce- and discover new fruits and vegetables along the way.
It's a good idea to plan your meals for the week, and to look for opportunities to make the most of the ingredients you have on hand, with the goal of not wasting anything. for example, if the salad you are making on Monday calls for half a bunch of scallions or basil, look for a soup or stir-fry to make later in the week that used up the rest. Also, take inventory of your pantry at the beginning of each week and stock up on wholesome basics (including grains, legumes, onions, and other alliums) that serve as building blocks for healthy meals.
Cook once, eat twice
By all means take advantage of "big batch" cooking: Roasted vegetables can be incorporated into a salad, tossed with whole-grain pasta, or folded into omelets. Dried beans or legumes are always good make-ahead options (they can even be frozen in single servings), as are whole grains and breakfast favorites like granola and museli.