You don't need to charge it for 8 hours like how we were taught previously. Just start using it as per normal and charge when necessary.
It is recommended to fully discharge the battery and do a full charge once a month to maximize battery life(use till below 10% and do a full charge to 100%)
The myth of DO NOT leave the power adaptor plugged in all the time is no longer true - macs are smart enough to stop charging when it reaches 100% or maximum full charge. but if you're paranoid, just pull it away - the magsafe connector makes it easy to connect/disconnect the power adaptor.
refer below articles for more details on batteries on Mac Portables
https://www.apple.com/batteries/maximizing-performance/#macbook
Mac notebooks: All about batteries - Apple Support