Here are the three most important tips I have for good battery on the GN3:
Reboot daily, and do it when the phone is fully charged AND STILL ON THE CHARGER! Let it sit on the charger for a good five minutes so it goes through the whole boot process without taking any battery usage. Rebooting cleans out caches, closes down programs, apps and widgets that might be running that you don't know about.
Screen brightness - find the best (lowest) screen brightness you can live with and set that as your fixed screen brightness. Using Auto-brightness is NOT a good battery saver and can be annoying as it changes your screen brightness as it feels like it with often annoying results. I use a free app called Brightness Level Disc that comes with a free widget that I put on my front screen. I run my screen at around 49% and get great battery results with that. If I need brighter or dimmer depending on ambient light, the disc has a neat four button switch to select brighter or dimmer with the press of a button on the front screen (or wherever you want it).
Last, but not least, your GN3 came with a neat little widget called Active Apps Manager. I also put this right on the front screen. It's a little number inside a circle. The number is for how many apps are currently running in your phone's memory. The circle around the number turns colors from green to orange to red. If it's red then at least one of your running apps is using the cpu and therefore battery. If it's green then the apps are idle and not using much battery. You can press the button and it will show you what apps are open and what percentage of cpu is being used.
This little widget is invaluable in telling you which apps are notorious for using the cpu (and battery) even though you are not actively using them. It helps you understand which apps you need to kill off each time you use them. For instance I have found that almost all my news apps that have notifications activated will continued to run and eat battery. Also, my chess app, Chess.com. So now I just know to kill them off after I'm done using them.
I do not turn off any of the other things suggested at the beginning of this thread. I leave on wifi, bluetooth, gps, 4G, syncing - you name it. I do not use live wallpapers as they do eat battery and I find them silly anyway!
Try these three things and you will be surprised how much better your batter life will be. If you do all three and your battery is still eating then you likely have a bad battery. I use my phone ALL day, texting, skype, phone calls, stream music for hours, chess moves, facebook, and I still have usually 20%, give or take 10%, at the end of each full day.