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For knowledge workers, there is a lot of work to do defining our work before we can start actually doing our work. The 5 phases of workflow is the GTD model for capturing, defining and doing our work.
The practice of setting aside dedicated time (typically a couple of hours) to make sure your system is clean, current and complete. David Allen regularly cites this as the critical success factor for GTD.
The practice of keeping strict boundaries between items of different types. In GTD, for example, it is highly recommended to keep reference material (which has no emotional cost) separate from commitments and actions you need to keep (which have strong emotional pull). If you blur the edges between items of different types, your system will not be effective.
A mechanism to remind yourself of something at a given time in the future. When the time arrives, the contents of the tickler file are moved into an inbox for processing with all other stuff.