ok, we will assume that you are planning for one week.
Look at your calander. Are there any nights when cooking is well nigh impossible? For us Wednesday is hard because we have Violin lessons, Church and JBQ, so that night I plan for eating take-out or making something super easy (like sandwiches or cereal) Next I put each meal I want to make on a day, and then check what ingredients I have in my cupboard for those things I want to make, and make my grocery list to include
*every single ingredient* that I need for those recipes so that I don't have to go back to the store.
Now that you've done that, add snacks, and breakfast/lunch foods to your list, and you're ready to go to the store.
Buy all the ingredients. When you get home, put them away in a way that makes sense to you. Do not hide anything from yourself!
The first week, resolve to stick to your meal plan, no matter what. Actually, it's good not to deviate too much from it for the first three months, with exceptions for emergencies, until you get good at it.
At first I would look at the calander and think "I don't really want that tonight
" but then I would remember that I would have to think of something else, and have the ingredients OR I would have to swap it with the food from another night. I have the stickie notes so I can swap food nights pretty easily, so I do that occasionally, but generally speaking, I just make the food I have on schedule.