The method I describe here is adapted from David Allen's very popular, very influential productivity system which can be found in his book Getting Things Done. It's written about extensively online, especially in the corners occupied by folks who are part of the "gig" economy and by freelancers, people who must manage several projects over time with different deadlines and components. If you are interested in productivity systems (as I am), you can find that they become an end in themselves. They can be fascinating and, if you're inclined to search out solutions, hold out, like diets, the irresistible flavor of hope possibly fulfilled.
I'm fond of David Allen because in his interviews and writing he strikes me as a practical man who is interested in the success of others. His approach makes cognitive sense to me. He urges folks to adapt as necessary. He expresses his system in terms of principles as well as practices, which makes adopting and adapting them easier, it strikes me, especially if you are, like myself, someone who needs flexibility project by project. One principle seems to me fundamentally sound: if you can put something down on paper, you'll be less likely to perseverate or to be intruded upon by a unfinished tasks. If you put something down on paper, you feel a sense of control over the tasks at hand, in part because you can analyze it more carefully and in more detail, and in part because you can reflect upon it in some other context than "right now". That is, if you tend to choose tasks based on a feeling of urgency, writing down what you must do allows you to reflect on the task, to map tasks on to time, and to choose your "next action".
I take a very simple approach to his system and have used what works for me and that is what I will introduce here. Two principles interest me: put it down on paper and reflect routinely.
In this section, you'll find material on Project, Next Action and Someday/Maybe lists. Without going into too much "inside baseball" talk in the productivity community about the work-ability of to do lists, Project and Next Action list provide a way to put it down on paper in a systematic way as the basis for a systematic way to reflect routinely. The Someday/Maybe list is a place to put ideas that occur to you while you are at work on other things (the perfect time for the appearance of good ideas) so that you are not distracted by them and so that you know your ideas is there to be worked with when more pressing tasks are completed.
For further reading on Project and Next Action Lists, see the "Reading" link under "Getting Things Done". Sample Project and Next Action Lists can be found here.