Simple Guidelines for iPod Battery Usage (as taken from BatteryUniversity.com)
Avoid frequent full discharges because this puts additional strain on the battery. Several partial discharges with frequent recharges are better for lithium-ion than one deep one.
Recharging a partially charged lithium-ion does not cause harm because there is no memory. (In this respect, lithium-ion differs from nickel-based batteries.)
Although memory-free, apply a deliberate full discharge once every 30 charges to calibrate batteries with fuel gauge (the battery life indicator). Running down the battery in the equipment does this. If ignored, the fuel gauge will become increasingly less accurate. The battery life will not be affected.
Keep the lithium-ion battery cool. Avoid a hot car. Short battery life in a laptop is mainly caused by heat rather than charge/discharge patterns.
For prolonged storage, keep the battery at a 40% charge level.