Useful Hints for Software Project Planning?

staaktdenarbeid asks: "Over my software-writing career, I noticed that development efficiency closely follows the 80/20-rule. That is, 80% of the progress is made during 20% of the time. The rest of the time, er ...well you are waiting for the next big idea. No matter how well planned a project is, it turns out that true progress is only made at very few points over the entire project lifetime. I would like to ask other Slashdot developers for their experiences, and if they know (and apply) project planning techniques that create a smoother development path."