I've noticed a couple of people on here asking about this, which is expected, since several people are just now getting their phones, and understandably want to take care of them (and their batteries) as best they can.
I got a super extended battery for my TP in late August, and asked this very question when I was trying to figure out how to best care for it. (It wasn't cheap.)
The basic answer, from several reputable sites in a Google search (One big one being
Battery University) is below. Note that the linked page makes reference to Li-Ion batteries 'with charge indication' - This means batteries with buttons on them that you can press to get a general reading on their charge level, something that does not apply to our phones.
If it makes you feel better, fully charge the battery before you do anything to discharge it. Not only does this put your mind at ease, it gives you more time to play around with the phone the first time you turn it on.
After that, keep the battery as fully charged as possible. Li-Ion batteries will manage their own charge currents (how much power the charger gives them) when full, so there is no danger of over-charging. However, Li-Ions do not react well to being discharged. The closer to dead they are, the worse it is. If the cell voltage falls below a certain point (Which the phone stops well short of, but it's still possible in theory..) then the battery will not be able to be charged with a standard charger. A specialized charger may be able to recover it, but this is not guaranteed. Batteries in that state sometimes short circuit/heat up dangerously.