Press the power button for about 10 sec to really turn off as opposed to "pretend turn off." Then when you plug it in, it will not boot, and you will just see the battery icon that shows charge status.

Normally when you power off (not just turn of the screen but press till it shuts down) it is not entirely off but not booted. You have to press for a longer time to get it to completely turn off.

This is good to know if you want to store the device without using it for a while. It is better to have it completely off. If you don't, and you plug it in, it may deplete the battery too low by trying to boot, which uses significant power. If your battery was very low from storage, this could cause problems because it is a pain to get the battery to start charging if it is too low; see other threads for reviving battery in such a case.