My GTD tip is a modification of the "Two Minute Rule" (TMR). I think of it as a meta-Two Minute Rule, or mTMR. mTMR means that I shouldn't spend more time inserting an action into a tracking system, than is required to complete the action. So, mTMR isn't about the specific number of two minutes, but as many minutes as it would take to record and track the action.
Thus, if it would take twenty minutes to set up a project, but fifteen to complete, then that project is subject to mTMR, even though it takes more than two minutes. If it isn't appropriate to do a fifteen minute action right now, it can be inserted as a next action, even if it has multiple steps.
The trick (for me) is to avoid the overhead of tracking it as a project, if the tracking overhead will cost more than the project itself.
Cannonical GTD has the TMR:
If action takes less than two minutes, then do it.
My "mTMR" replaces this with the idea:
If Tracking Overhead > Estimated Action Time
then do action without inserting the action into a tracking system
else insert action into the tracking system