One of the best things I do for myself every week is to make a weekly meal plan, complete with shopping list, and stick to it. Spending about 15 minutes looking through my recipe binders every Saturday night saves me tons of time (and last minute grocery store trips) during the week. I plan my meals and make my list, and then every Sunday I do my grocery shopping to get what I need. I use one of these handy little planners, but you don't have to. A piece of notebook paper works, too.
The trick to making the plan work is to take into account that particular week's events (I usually write them right on the meal plan paper). For instance, every Thursday night B has Brownies and we usually get home around 6:15 or later, so I know I need to plan an easy and fast meal for Thursday, or else I need to prepare most of the meal ahead of time so that I can just put the finishing touches on it when I get home.
I also try to write in any special events that will take us away from home on any given evening. That way I won't be buying food for a meal that won't get made.
Probably the best thing about planning out my meals a week at a time is the luxury of going into the kitchen to make dinner and knowing beyond a shadow of a doubt that I have everything I need right there. Nothing makes me cranky faster than having to run to the store to pick up a can of diced tomatoes or cilantro right at dinner time!