Thank you very much, David Allen. I'm finally going to get organized!
By asking "What's the next action?" one transforms a big, scary project one has been procrastinating into a simple, doable first step. It makes things easy and fun.
Allen says "You have to think about your stuff more than you realize but not as much as you're afraid you might." In this system, any project needs at least two things: an entry on a list of projects, and a specific, physical "next action" on a list of actions that can be done in a specific context, e.g. at home, at work, on the computer, etc. It usually takes a few seconds of serious thinking to transform an amorphous project into something with a doable "next action" identified; for example, if you've been procrastinating putting your bike in the shed for the winter, it helps to identify the first physical action as "check whether key to bike lock is in key jar".
Any "next actions" that will take less than two minutes, and can be done right away, one does right away. Doing a few of these gives a feeling of freedom and relief: things are moving.
It's a low-guilt system because you keep on your lists only things you want to be reminded of. When choosing an action to do he says to consider context, time and energy before priorities. That way you can still get some useful things done even when you're tired.
If you try to just keep track of things in your head, aversive feelings of frustration and discouragement get associated with your projects in your mind as you tell yourself, "I don't want to think about that right now, because I can't do anything about that here and now." Allen says his system lets you have a "mind like water". You don't need to worry about things; you can focus on one thing at a time. You present yourself with lists of things you actually can do, and likely want to do, in a particular time and place, which gives you the feeling that things are moving, like the well-oiled wheels on the properly-working filing-cabinet drawer that Allen also recommends that you have.
As part of Allen's system, I'm using a tickle file, and it's working beautifully, even though it had failed dismally when I tried it years ago. A tickle file is basically a file folder for each day of the month and each month of the year, for sending yourself reminders. One reason it's working is I'm applying Allen's advice about calendars: to use them strictly only for things that are intrinsically more appropriate at some later time than now, not for things you just don't have time for now. I also try to have at least one item per day so it's not boringly empty, and to include fun, positive things such as songs I'm memorizing or letters of thanks I've received. I put some of the reminders on coloured cardboard, just to make it more pleasant. And finally, I make it easy: instead of necessarily doing the things immediately, I can put them on a list or decide not to do them.
I've used many systems, and usually tried to avoid overloading a system with too many "to-do's" in case I won't want to look at the whole system. But Allen's system makes things easier by identifying doable "next actions", and has a safety valve by letting you move things off onto a "someday/maybe" list (while still reviewing that list regularly). I'm confident that, as Allen claims, it can be used to manage all one's stuff.
Allen's system meshes well with Ternouth's system. Both emphasize the importance of paper for helping you think, and both involve using an inbox and keeping it empty. I'm writing names of small projects on whole sheets of paper as Allen suggests; as a tree-hugger, if I complete the project without writing more than a couple of lines, I use an erasor so I can re-use the sheet; erasing is easy since I happen to like mechanical pencils with 2B leads.
I've been really enjoying using Ternouth's clear-desk system. The freedom is great: you can spread out the papers of one project however you want on your nice, clear desk, allowing your brain's artistic/visual capacity to interact with the papers. But you have to put them away again before getting out another project or going home: a discipline which only takes a few seconds once you get used to it. It's great having that clear desk to put things on. (What else is a clear desk for, except to put things on? :-) Ternouth might not be impressed: I have a clear desk. I also have other desks with piles of papers on them, but I have a clear desk...
Ternouth's system involves flipping through papers to rapidly absorb information, reviewing papers regularly, and discarding papers but reviewing many of these a month later to make sure nothing important is missed. His description shows great respect not only for the importance of paper but also for the way our minds work, and is well worth reading. A big "thank you" to Martin Ternouth, too.