With lithium-ion batteries, there's no need to charge/drain your iPhone on first use. It is, however, recommended that you discharge and recharge once a month.
Just use the phone normally as you would. No need to completely drain it out of the box. I never drain my battery and battery life is great and reporting no issues here.
Basically don't leave the phone plugged in all the time, try to keep it above 20%, do your best to keep it from getting super hot (leaving it in the sun), and enjoy!
I've found turning off the % indicator has added to my enjoyment of the phone.