I think there are some Forrester notes on Wikipedia regarding shifting.

Personally, I shift as I would in a car. When I start out, I'm in the lowest gear (of the range I typically use for road riding, top front cog and 1st-3rd on the back) and then as I start to get into a higher cadence, I shift up and so forth. Then, when slowing for a light (and you know you're going to stop) just shift down, if you're rolling in and think you can get a head start, obviously don't shift all the way back to your 'start' gear, you'll just feel which is right and go with it.