Think about it, organize things, but your direction will change many times in how you code a project, so will how you organize that project. Just remember that and try and make things as clear as you can when you do any larger parts and you will be fine.
I tend to do a mix, thinking about how it will be and making blank functions and files for them, but that always tends to change at the end of the day and find myself changing function names all the time.