As suggested, many people notice their battery life increasing in the first few days, ect. This could be due to either battery life increasing or sensor calibration becoming more accurate.
The app 'spare parts' can be useful for troubleshooting battery issues and tracking down rogue apps because it allows you to look at 'partial wake' usage, which is different than looking at what is hogging the most power when the phone is awake/on. An app that tries to geolocate every so often and hence keeps the phone out of a battery-saving sleep status while activating power-hungry radios might not draw a ton of power itself, but could impact battery life by disrupting natural battery conservation strategies. (As I understand it...)
Also, rogue apps can be a huge battery drain. The only one I've ever had that affected (seemed to knock my battery life by half) was ironically a battery status widget called BatteryLeft.