It is recommended that you let the Lithium-Ion battery charge for 12 hrs straight when you first get the battery. Then, use the computer (on battery power) over time until the battery depletes, causing the laptop to go into sleep mode. Then you can plug it in and charge it until the LED turns green (4hrs or so).
You may now partially deplete the battery, plug it in, partially deplete it etc... Lithium-Ion batteries do not suffer from the memory effect and therefore you may freely switch back and forth between AC and DC usage. However, every 2-3 months, it is recommended that you fully charge the battery and then fully deplete it again.
If you ever stop using the system for more than a month, remove the battery from the computer to store it for an extended period.