This page has some notes on the Raspberry Pi 3. Note that it's basically exactly the same as the Raspberry Pi 2.

Installing

Image

I utilized the image ubuntu-16.04-preinstalled-server-armhf+raspi3.img from this link: https://wiki.ubuntu.com/ARM/RaspberryPi

Everything's pretty straightforward, once you've written the Pi image file onto the SD card, you plug it in and you fire it up.

Anything you want to run on startup should go in /etc/rc.local

If you want to start wifi on boot, you can add the wireless network name and credentials to the /etc/wpa_supplicant/wpa_supplicant.conf

Alternatively, you can turn on wifi sniffing on boot, by putting commands to put your card into monitor mode into the file /etc/rc.local

Here's the sequence I use:

ifconfig wlan1 down
iwconfig wlan1 mode monitor
rfkill unblock all # optional 
ifconfig wlan1 up

This brings the wireless card up in monitor mode, where it does not discard any wireless packets received.