While efficient hardware and software can help preserve energy, the greatest drain on your laptop's battery will largely be the programs that you use. For instance, if you decide to encode a lengthy high-quality movie file, then you will ramp up all cores of your processor to their maximum, and even on a full charge, you will be left with a short amount of battery life available.
To help preserve battery life, in OS X Mavericks Apple has implemented features like App Nap to pause unused programs, and CPU timer coalescing to allow processors to maintain a lower average energy usage. In addition to these automatic features, you can use common power-saving methods such as dimming your system's screen, and disabling unused hardware like Bluetooth and Wi-Fi controllers. However, the benefit of these steps will be nullified if you have a program that is computationally demanding.
To look this up in prior versions of OS X, you would mainly use Activity Monitor's %CPU usage calculation. However, without careful observation you might mistake a brief burst of activity from one program as being something more extensive causing the battery drain.
In Mavericks, Apple has offered ways to help you better assess poor battery life. If you select the Energy section of Activity Monitor, you will see a default column labeled "Energy Impact" that is a relative measure of the power used by that program's demand on the system's hardware. Sort the process list by this column, and any that show persistently high numbers might be worth closing down to maintain battery life.
Note that by default, the Energy section of Activity Monitor only shows user applications run in the past 8 hours, which will overlook background processes that might also be contributing to lower battery life. Therefore, go to the View menu and choose "All Processes" to get a better view of what is running.
In addition to the Energy Impact rating, you can sort the list by the column labeled "Requires High Perf GPU" to see which programs are keeping the system using the more powerful (and more demanding) graphics card on systems that ship with two. If the Graphics Card status in the Energy view shows "High Perf." then you can try locating and quitting any programs that say "Yes" in the "Requires High Perf GPU" column.
Lastly, while Activity Monitor is a great tool for assessing process load, you can also look up the applications that have a significant energy impact by opening the Battery menu extra (enabled by checking "Show battery status in menu bar" in the Energy Saver system preferences). You may have to wait a few moments, but then you will see a listing of apps that are using significant energy. Selecting one of the listed applications will open up Activity Monitor with the program selected, so you can see other statistics about it.