I first learned about Power Management through this website:
It is a good overview of how everything works.
While focused on Thinkpads mostly, this page is also very helpful:
Power Management on Computers running the Debian Universal Operating System
On laptops and small service machines which run 24/7 I install:
apt-get install acpitool
and I add this to /etc/rc.local
echo "/bin/echo 1500 > /proc/sys/vm/dirty_writeback_centisecs" >> /etc/rc.local echo "/bin/echo 5 > /proc/sys/vm/laptop_mode" >> /etc/rc.local echo "hdparm -S 12 /dev/sda" >> /etc/rc.local echo "modprobe acpi" >> /etc/rc.local echo "echo 'ondemand' > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor" >> /etc/rc.local
Powertop
Powertop is a great utility for linux to get an idea of what is causing your processor to wakeup. It was written by Intel and takes advantage of newer features in their CPUs.
sudo apt-get install powertop sudo powertop
Powertop will display a "top" like scoreboard, identifying some processes which are chewing up energy, as well as suggest helpful ideas to reduce power consumption.