While I've focused on some of the big items that affect a home's energy efficiency, there are many smaller items that also play a significant role, if only because there are so many of them. Take a look around your own house and count the lights, computers, TVs, etc. that use electricity on a daily basis. These things combine into what I call the base electric use of the home. A couple of years ago I was getting interested in electricity use in our house (because our utility bill was enormous), so I decided to go through each room, and write down every piece of equipment that consumed electricity. There were a lot of them. I then decided I wanted to know approximately how much energy each one of them consumed. With light bulbs, that's pretty easy. For some appliances, I could look up the rating to get an estimate. Others I had no way to estimate.
Fortunately, there are tools available to help. I bought an inexpensive energy meter that displays the number of watts used by a device plugged into it. There are several manufacturers that make these devices, the most common of which is the humorously named Kill-A-Watt. With this device I was able to go through every room and come up with an estimate for each device.
That's the point at which I switched the majority of our light bulbs to CFLs. We had light fixtures that used five 60-watt bulbs in our living room and bedroom. By switching to 23-watt bulbs, I was getting the equivalent of 100-watt lighting for a third of the electricity.
Perhaps one of the most surprising finds was the UPS (uninterruptible power supply) for my computers. At the time I had two computers (one for personal use, one for connecting to work), with a nice 24-inch monitor and all of the usual peripherals (printer, speakers, etc.). I wasn't very good about shutting them down every night, but it never occurred to me that just having the UPS in the "on" state was consuming a lot of power. It turned out that the UPS was consuming about 100 watts, and it was on 24 hours every day. That was contributing 72 kWh every month (about $8). Fortunately, there was a button on the UPS that allowed me to turn it off so that it wasn't consuming more than a couple of watts.
With just a few changes, I had reduced our electricity consumption by about 10% (and that was 10% of peak summer use, not the base electric use). Then two months later, we had to replace our air conditioner, upgrading from 12 SEER to 14 SEER. While I wouldn't have chosen to spend the money to get better efficiency, it turned out that the 14 SEER was the same price as a replacement 12 SEER, so it was essentially a free upgrade (although calling spending several thousand dollars "free" is pushing the meaning of the word).
The net result was that our bill was 20% lower than when we started the process.
Since then, we've built our new house, and I keep track of everything that gets plugged in, and I have at least a fair idea of how much energy each item consumes. I also know which devices are the worst offenders (two set-top boxes for cable TV - they consume about 20 watts each, even in the "off" state), and keep an eye out for ways to replace them with more efficient devices, or eliminate them entirely.