This is a simple step-by-step guide for flashing a minor update (e.g., monthly security update) and re-rooting for Nexus devices.
This is meant to be more of a reminder checklist for those who do this semi-regularly; if you haven't done this before or don't know much about adb and fastboot, you should probably find a more detailed guide (see here for the Nexus 5X or here for the Nexus 6P).
The easiest way to update your nexus device manually is through the OTA downloads provided by Google.