It's hard to do, but really try to ignore the tendency to close apps.
Android is designed from the ground-up to do the battery and RAM management for you. You just don't have to worry about it. However, from time to time, you there may a situation where an app may crash and inadvertently use up CPU cycles. When that happens though, you'll know right away as your battery life will be much worse. You can close those apps when that occurs.... but it's pretty rare.
Also I'd recommend investing in an extended battery if you hate watching the battery meter drop. They increased my average battery life from 1.5 days to about 4 days... very much worth it if you ask me!