Good evening all - I hope you'll entertain a question from a newbie.

I looked through the FAQ section and may have missed a thread like this - if I did, my apologies.
I'm wondering how closely you plan your eating day-to-day. I'm not a very good planner - can manage to plan dinners for a few days at a time at best - and I think this may have been one of my downfalls in recent months.
My DH and I plan to begin South Beach tomorrow, and I made a big shopping run today for staples. I planned dinners and stocked up on salad greens, meat, the right cheeses, eggs, and things like that to use for lunches for the next few days. I didn't plan breakfasts and lunches because I'm so accustomed to eating something that sounds good rather than something I planned, and I didn't want to set myself up for an unfulfilled craving, you know?
So I'm just wondering how you structure your weeks. Tell me what helps make you successful.
Thanks in advance.