iPhone charging - tips?

Okay so yesterday my iPhone 5 was pretty much charged fully out of the box.

With my iPhone 4 I charged it fairly often and I think I killed the battery.

I get that you're supposed to drain it and recharge fully once a month but how do you charge?

Is there a certain limit you let it fall to before you plug it back in?

Can any of you give me some tips please, don't want to mess around with this battery.