Keep your drive defragmented and your files well placed. I used to use MyDefrag but have since moved to UltimateDefrag. Both are very good; MyDefrag is scriptable (complicated but highly customizable) and UltimateDefrag presents a sufficient subset of scriptable features in a nice interface.
If you have the discrete GPU, get nTune and underclock the GPU when running on battery power. I think some other third-party tools can also do the trick too.
Watch Resource Monitor's CPU and Disk tab for activity while idling; replace software that consumes significant rogue CPU cycles while idling or randomly pokes at files while idling.
These points will bring the most significant power savings, IMO.