Not Getting Things Done
The most important part of Getting Things Done (GTD) is not getting things done. The part of the process where you ask yourself if something actionable, there are time when the answer is no. I'll be brave and venture to guess that the answer is more often no.
If you don't have a good system for processing the noes, the noes will creep back into your head-space. No should mean no. When no action is needed on your part, you have to trust that your system will handle no as no.
Too often noes piles pile up waiting to be dealt with officially. One example is mail that needs to be shredded before going into the trash. Any mail that ends up in a pile that is "to be shredded" is not a true no. It's waiting to be off your list. One day when you dig out the paper shredder from the closet and shred that pile, then and only then will it be a valid no.
Noes need a home just as much as yeses. Noes can find a home as trash, an incubator, or reference file. Items that have no immediate action need to make a fully committed migration to their new home. Items that are trash are done when they are in the can.
Items that are on a some-day or a maybe-list need special attention because they occupy the most head-space. These are typically wild ideas and concepts that are appealing and interesting. Some day it would be wild fun to restore a classic car... and while it is fun to daydream about that, it is best to note it in your incubator and move onto what needs to happen now. Your incubator is there for your review as often as needed; the ideas will not be lost.
Reference materials are a pain due to volume. The items that we collect as samples or reference pile up fast than they can be filed... leaving piles everywhere. One of the more difficult part of reference materials is the lack of consistency in size and shape. For paper based materials, sometime converting to a standard size is the most helpful; this can be done with a simple Xerox. For large and odd items, a digital photo may be all you need. Aggressively seek to get items filed before the piles bury you.
While the rest of the world is struggling to get ahead by focusing on the yeses, refine how you handle your noes. The impact can be huge, particularly for those with a real handle in the yes-side of things.