There are basically two kinds of to do lists. You will need both.
The first kind of list is everything you need to remember to do. This is sort of a task oriented bucket list and it can be very long. This is the specialty of David Allen’s Getting Things Done (GTD) approach to productivity. I know of no better way to inventory everything that is in the warehouse of what needs to be done. As David Allen notes, you need to move these tasks from your mind to paper or they will continually distract you and rob your mind of processing power. This is an inventory of everything you need to do.
At the far other end of the spectrum is the concept represented by Kanban, a Japanese manufacturing process which understands that workers only need to focus on what is directly in front of them right now. Other people in the manufacturing chain see to it that you have each item as you need to work on it, withdrawing it from inventory only when necessary. This allows for the maximum focus.
Each day there are certain things you need to do. I like to call these my big rocks, based on the famous story Stephen Covey tells. You have to get the big rocks first or you can’t fit them into your day. Stephen Covey likes to keep the big rocks in the order by organizing the list for the week rather than the day. This makes it easier to choose between your big rocks.
The simplest system is the one advocated at the link below. As you begin each day simply identify the three most important things. Start with number 1 and finish it. Then start with number 2 and finish it. Then start with number 3 and finish it. Then crumple up the list and do as you wish with the rest of your time. If you accomplish the three most important things to do each day, you will be well ahead of the rest of the world.
The dark side of a to do list that is 2 long is that going to leave you with a sense of desperation and anxiety about ever finishing everything. This can lead to avoidance and procrastination. David Allen GTD handle this by identifying the next action in each pile of tasks. It is possible, still, for the list of next to actions to become overwhelming. And the priority of a task some time is lost or blurred due to the sheer quantity of things to keep track of on paper in a bucket list.
Why not keep both lists?
The Best To-Do List You’ll Ever Make
by RICK BROIDA from http://www.cbsnews.com/news/the-best-to-do-list-youll-ever-make/