What I am about to say, applies only to notebooks with Lithium Ion batteries (98% on the market). If you take a a look at your battery, it should say Li-Ion, or similar. If its says Ni-MH, then ignore below.
Lithium Ion battery packs do not have a memory effect, nor are they effected by the charging/discharging cycles. Essentially, it does not matter whether u repeatedly drain it down to 20% before recharging, only use 10% before recharging, or whether u widely vary how you use the battery. For example, typical use of a laptop might be -
Discharge to 50%
Charge back up to 95%
Discharge down to 20%
Charge back to 45%
Discharge again to 15%
Fully charge to 100%
which the battery is perfectly happy with.
etc etc etc.
In other words, dont worry at all about how you use the battery/discharge it.
HOWEVER, if you use your laptop in a situation where its plugged in long term, and the battery is not used often, it IS a good idea to remove the notebook battery, and plug it back in every few weeks or so for a top-up.
ALSO, do NOT fully discharge Lithium Ion batteries e.g. below 3-5%, but I'm sure your laptop's power managmennt would have kicked in and shut your laptop down at 8% or so anyway.