battery - When should I charge my laptop?

I was wondering how often should I charge my laptop?

I have heard that using my charger plugged in will cause the battery to heat up and reduces battery life. Thus I've decided to stick to using my battery, since it is here for a reason. (my battery is built-in, non-removable).

However, I am not sure when I should charge my laptop, and do I charge it to 100%?

Should I charge my laptop only when the battery dies out (0%) or is there a reasonable point I can let it run down to? (10% or something?)

My Battery: 47WHr battery; 6-Cell Li-Polymer (built-in)