Always assume that a battery you just got was on the shelf for months, so condition it. Charge it fully (the phone will tell you when it's fully charged) then another half hour. (Due to the way we have to measure state of charge, "100%" is actually about 98% if the charger wasn't connected.)
Then use the phone normally, turning it off when you normally would, until the phone tells you to charge it again.
Do that 3 times - full charge, then discharge until the phone complains.
After the 4th charge, you can use it as you like. (But after conditioning it, try to never let it fall below 40% - the more you let it drop below that, the shorter the battery will last. If you try to drain every lkast bit of power from it every time, you could destroy the battery in a month [and the battery isn't covered under the warranty].)