I sit down one night and plan my meals for at least a week ahead and get all the ingredients in. I make the complicated ones when Ive got most time eg weekends and have easy stuff like salads or Quorn stuff & veggies/SW chips when I have less time.
In winter I make soups/casseroles/stews/cottage pies in vast quantities and freeze them. Also, slow cooker - bung a massive pot on in the morning, it'll be ready for your tea when you get in and then you freeze the leftovers for another night or have it for lunches.
I keep lots of Quorn burgers/sausages (or equivalent) in the freezer that I can have with beans/veggies/SW chips or whatever if I've not had chance to get anything else in/not time to cook properly.
Similarly loads of dried pasta/lentils/beans that I can make into curries/salads/stews (and freeze leftovers of).
In summer each week I get about 5 lettuces, 4 tins of chickpeas, 1.5kg bag of carrots, 3 boxes tomatoes - plus snap peas, baby corn, Quorn slices or whatever to go with it - so I can make enough salad/hummus for a weeks worth of lunch plus some teas/side dishes for tea.
Its all in planning ahead for me, planning for the next day is not enough, I plan at least a week ahead.