I just keep a charging dock on my nightstand and put my phone it in every night regardless of battery level.
I also keep a charger in my car just in case.
Finally I have a dock on my desk at work. So i'll throw it in there throughout the day if I remember.
Since i've had my blackberry, I have only once been concerned about the battery level. That is because I drank too much and forgot to throw it on the charger at night and the next day I was out the door early and no where near a charger.