I haven't done anything special, but I know the Nvidia card is basically off all the time, and the DVD drive powers down and off within about 30 seconds of startup. I have maximum power saving settings under the advanced settings of power manager. I'm usually using Word, Outlook and Web, so not putting anything very strenuous on the CPU, which is Core i7-2640M @ 2.8 GHz (I think the M maybe stands for Mobile, so that may make a difference). I have the best screen available for the W520 (1920 x 1080). I have Wifi connected to a router that has robust power saving. And an Intel SSD, so the machine is very, very quiet -- the fan is either off all the time or on such a low setting that I can't hear it (occasionally I can feel cold air drifting out of it). Apart from that, and keeping the screen brightness around 10, I can't think of any special configuration.
(Before anyone asks why I got a powerful machine like this to do office work at low power, I got it because it's the last Thinkpad with a real keyboard

, because of the incredible build quality, because I want a machine that will last several years, I want the option of high power when I occasionally need it, plus I needed fast USB 3 for connection to external hard disk and the T520 didn't offer that if I remember rightly.)