Exercise caution. Depending on when the vehicle was driven, temperatures under hood could be high enough to cause burns.
Prerequisites
First thing first, shut off the engine and turn off the ignition.
Open the hood and the trunk.
Close the doors.
Unplug the battery (or both if required with two). Alternatively, lock your vehicle using the keyfob, leave the hood/trunk open, and walk away for 10 minutes. This will allow the vehicle to enter full sleep mode and power down electronics. When coming back to the vehicle, leave the keys away so as not to wake up the vehicle.