On a radio program, I once heard of this method, invented about 100 years ago by Ivy Lee.
At the end of each workday, I write down a maximum of the six most important tasks I want to complete the next day. The most important task goes on top.
When I start the next morning, I try to work on nothing else but the first task until I completed it. Then I move to the next task, and so on. What I did not complete by the end of the day becomes an item of the list for the next day. I do this every working day.
This method works great for me, probably because it is so simple. I like simple.
There is also a nice story behind the Ivy Lee Method.