Apple had a bad batch of batteries a couple of years ago. I believe they will replace them for free if it's one of the bad ones.
I find that the biggest battery drainer is the retina display. I keep the brightness turned down as much as possible and still be able to see things. #2 is leaving a graphically intense game running in the background. I never just close a game, I kill it using the swipe up method (seems to be kinda similar to Windows 8 to me).
Some people will say the cellular modem drains the battery fast too but my experience from using it as a cellular hotspot is that I can go for over 12 hours with the display off and still be at 70 something % of charge.
I found an app that no longer works on 7. It's an audio recording program, and the new version costs 2.99! Today was the first time I've tried to use it. So I guess I really don't need it.