A shopping cart full of thoughts

When I go to the grocery store with a list, it always takes me longer than it would take my wife with the same list. Unlike me, she knows where everything is in the store. So she goes aisle by aisle and proceeds efficiently. Me? I look at the first thing on the list and zig-zag all over the store until I find it and then look at the second thing and zig-zag all over again. It is like walking through a maze.
In our writing, if we have not set a clear path for the reader, he or she will also feel like they are walking through a maze. The difference is, a reader can easily get out simply by refusing to read any more.
The second reason it takes me longer is that in my zigging and zagging, I find other things besides what are on my list and toss them in the cart. In writing, imagine the poor reader if every time we came up with a new thought, we tossed it in the cart with what we had carefully planned.
Here's a simple way to organize our thoughts. After you have determined your subject, write your "shopping list" - a numerical list of everything you want to include. For instance, if you were writing about Abraham Lincoln, you might write:
1. boyhood; 2. slavery; 3. Civil War; 4. wife and family; 5. Lincoln-Douglas debates; 6. presidency; 7. assassination...
When you've completed your list, probably 20-30 thoughts, go back through and put them in groups. In the Lincoln example, Nos. 2, 3 and 6 and 7 might go together in one group and Nos. 1 and 4 in another group.
Once you have them grouped, prioritize them. Which group do you want to write about first? Then what's next? And what's next after that?
That's how to fill your shopping cart. Try it. It works.