It has a lithium ion battery which does not like to be fully discharged often. It's actually better to recharge it before it gets too low. It's OK to frequently 'top it off."
In general, just use the iPad how you please and recharge it when it's most convenient. Don't intentionally run it down every time.
Heat is an enemy of the battery. Avoid prolonged exposure to high heat.
For more on Lithium Ion batteries, read here:
http://www.batteryuniversity.com/parttwo-34.htm
I've included the first 3 guidelines which are applicable:
Simple Guidelines
* 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.) Short battery life in a laptop is mainly cause by heat rather than charge / discharge patterns.
* Batteries with fuel gauge (laptops) should be calibrated by applying a deliberate full discharge once every 30 charges. Running the pack down in the equipment does this. If ignored, the fuel gauge will become increasingly less accurate and in some cases cut off the device prematurely.
* Keep the lithium-ion battery cool. Avoid a hot car. For prolonged storage, keep the battery at a 40% charge level.
Also see Apple's iPad Battery Page here:
http://www.apple.com/batteries/ipad.html
