Just bought the iPhone 6 plus how do I keep its battery life amazing for the next 2 years I have it?

My phone is still in the box and I want to know what I do to start its battery life off right? I heard some people say since it has a charge when you buy it to let it die and then charge it to 100% or some people say right when you buy it out it on the charger but i don't know WHAT's best? Can anyone help me out thanks!

Charge it to full and avoid complete discharge. They are mostly based on how many full charge to depletion cycles. So basically every time it goes through a cycle, it degrades a little every time. Or in short, here are some steps and a long technical study.