Welcome to Android Central! It actually doesn't matter -- with lithium batteries, you don't have to charge it fully before you start using it out of the box. There's no "memory," like with older NiMH batteries. In general, though, with a new phone out of the box, it's a good idea to charge it to 100% before using it, or keep it plugged in while you're setting it up, because the initial setup process can use a fair amount of battery (due to the phone installing a lot of your usual apps).