One quick thing before we start — 99.9% of the time it is not actually iOS that is causing your battery to drain quickly. I guarantee you that if you erased your phone and there were no apps or email on it, it would last for ages. But, no one uses their device like that, nor should they. Hopefully with these steps you will be living in iOS battery bliss while still using all the apps and features you love. Scotty Loveless
A great deal of sound advice here – and some counterintuitive steps, like Stop Quitting Your Apps in Multitasking, which I see people do all the time. Personally I used most of them already, for example I usually turn off cellular data when I’m at home and use only Wi-Fi; even if I have good signal this almost doubles the battery life. I also disabled location services and background app refresh on most apps, including Facebook, although for a different reason: since iOS 7, every time I start an app that uses location and I’m not connected to Wi-Fi, I get a pop-up reminding me to turn on Wi-Fi to improve location accuracy – very annoying! But it’s nice to know that this saves power too.