4. Setup ADB Udev Rule
Before accessing your android device in ADB mode, you need to :

set the device to use USB Debug
declare a corresponding Udev rule on your Ubuntu box
After setting the device in USB Debug mode and connecting it to a USB port, throw the command :

Terminal
# lsusb
...
Bus 001 Device 119: ID 2a70:9011
This is the result for a OnePlus 3 connected in MTP mode with USB Debug on. It gives  :

the Manufacturer ID
the Model ID.
To be on the safe side, we will declare some generic rules for main Android phones manufacturers.

These rules will be declared /etc/udev/rules.d/51-android.rules.

/etc/udev/rules.d/51-android.rules
# udev rule to detect android devices
# These rules refer to http://developer.android.com/tools/device.html

# Acer
SUBSYSTEM=="usb", ATTR{idVendor}=="0502", MODE="0666", GROUP="plugdev"
# Archos
SUBSYSTEM=="usb", ATTR{idVendor}=="0e79", MODE="0666", GROUP="plugdev"
# Asus
SUBSYSTEM=="usb", ATTR{idVendor}=="0b05", MODE="0666", GROUP="plugdev"
# Azpen Onda
SUBSYSTEM=="usb", ATTR{idVendor}=="1f3a", MODE="0666", GROUP="plugdev"
# BQ
SUBSYSTEM=="usb", ATTR{idVendor}=="2a47", MODE="0666", GROUP="plugdev"
# Dell
SUBSYSTEM=="usb", ATTR{idVendor}=="413c", MODE="0666", GROUP="plugdev"
# Fairphone
SUBSYSTEM=="usb", ATTR{idVendor}=="2ae5", MODE="0666", GROUP="plugdev"
# Foxconn
SUBSYSTEM=="usb", ATTR{idVendor}=="0489", MODE="0666", GROUP="plugdev"
# Fujitsu Toshiba
SUBSYSTEM=="usb", ATTR{idVendor}=="04c5", MODE="0666", GROUP="plugdev"
# Garmin-Asus
SUBSYSTEM=="usb", ATTR{idVendor}=="091e", MODE="0666", GROUP="plugdev"
# Genesys
SUBSYSTEM=="usb", ATTR{idVendor}=="d324", MODE="0666", GROUP="plugdev"
# Google
SUBSYSTEM=="usb", ATTR{idVendor}=="18d1", MODE="0666", GROUP="plugdev"
# Haier
SUBSYSTEM=="usb", ATTR{idVendor}=="201e", MODE="0666", GROUP="plugdev"
# Hisense
SUBSYSTEM=="usb", ATTR{idVendor}=="109b", MODE="0666", GROUP="plugdev"
# HTC, Wiko
SUBSYSTEM=="usb", ATTR{idVendor}=="0bb4", MODE="0666", GROUP="plugdev"
# Huawei
SUBSYSTEM=="usb", ATTR{idVendor}=="12d1", MODE="0666", GROUP="plugdev"
# Intel
SUBSYSTEM=="usb", ATTR{idVendor}=="8087", MODE="0666", GROUP="plugdev"
# K-Touch
SUBSYSTEM=="usb", ATTR{idVendor}=="24e3", MODE="0666", GROUP="plugdev"
# KT Tech
SUBSYSTEM=="usb", ATTR{idVendor}=="2116", MODE="0666", GROUP="plugdev"
# Kyocera
SUBSYSTEM=="usb", ATTR{idVendor}=="0482", MODE="0666", GROUP="plugdev"
# Lab126
SUBSYSTEM=="usb", ATTR{idVendor}=="1949", MODE="0666", GROUP="plugdev"
# Lenovo
SUBSYSTEM=="usb", ATTR{idVendor}=="17ef", MODE="0666", GROUP="plugdev"
# LG
SUBSYSTEM=="usb", ATTR{idVendor}=="1004", MODE="0666", GROUP="plugdev"
# Mad Catz
SUBSYSTEM=="usb", ATTR{idVendor}=="0738", MODE="0666", GROUP="plugdev"
# Meizu
SUBSYSTEM=="usb", ATTR{idVendor}=="2a45", MODE="0666", GROUP="plugdev"
# Micromax
SUBSYSTEM=="usb", ATTR{idVendor}=="1ebf", MODE="0666", GROUP="plugdev"
# Motorola
SUBSYSTEM=="usb", ATTR{idVendor}=="22b8", MODE="0666", GROUP="plugdev"
# MTK
SUBSYSTEM=="usb", ATTR{idVendor}=="0e8d", MODE="0666", GROUP="plugdev"
# NEC
SUBSYSTEM=="usb", ATTR{idVendor}=="0409", MODE="0666", GROUP="plugdev"
# Nokia
SUBSYSTEM=="usb", ATTR{idVendor}=="0421", MODE="0666", GROUP="plugdev"
# Nook
SUBSYSTEM=="usb", ATTR{idVendor}=="2080", MODE="0666", GROUP="plugdev"
# Nvidia
SUBSYSTEM=="usb", ATTR{idVendor}=="0955", MODE="0666", GROUP="plugdev"
# OnePlus Two (unknown vendor's name)
SUBSYSTEM=="usb", ATTR{idVendor}=="2a70", MODE="0666", GROUP="plugdev"
# Oppo
SUBSYSTEM=="usb", ATTR{idVendor}=="22d9", MODE="0666", GROUP="plugdev"
# OTGV
SUBSYSTEM=="usb", ATTR{idVendor}=="2257", MODE="0666", GROUP="plugdev"
# Pantech
SUBSYSTEM=="usb", ATTR{idVendor}=="10a9", MODE="0666", GROUP="plugdev"
# Pegatron
SUBSYSTEM=="usb", ATTR{idVendor}=="1d4d", MODE="0666", GROUP="plugdev"
# Philips
SUBSYSTEM=="usb", ATTR{idVendor}=="0471", MODE="0666", GROUP="plugdev"
# PMC-Sierra
SUBSYSTEM=="usb", ATTR{idVendor}=="04da", MODE="0666", GROUP="plugdev"
# Qualcomm
SUBSYSTEM=="usb", ATTR{idVendor}=="05c6", MODE="0666", GROUP="plugdev"
# Rockcwell Electronics
SUBSYSTEM=="usb", ATTR{idVendor}=="2207", MODE="0666", GROUP="plugdev"
# SK Telesys
SUBSYSTEM=="usb", ATTR{idVendor}=="1f53", MODE="0666", GROUP="plugdev"
# Samsung
SUBSYSTEM=="usb", ATTR{idVendor}=="04e8", MODE="0666", GROUP="plugdev"
# Sharp
SUBSYSTEM=="usb", ATTR{idVendor}=="04dd", MODE="0666", GROUP="plugdev"
# Sony
SUBSYSTEM=="usb", ATTR{idVendor}=="054c", MODE="0666", GROUP="plugdev"
# Sony Ericsson
SUBSYSTEM=="usb", ATTR{idVendor}=="0fce", MODE="0666", GROUP="plugdev"
# Spreadtrum
SUBSYSTEM=="usb", ATTR{idVendor}=="1782", MODE="0666", GROUP="plugdev"
# T & A Mobile Phones
SUBSYSTEM=="usb", ATTR{idVendor}=="1bbb", MODE="0666", GROUP="plugdev"
# Teleepoch
SUBSYSTEM=="usb", ATTR{idVendor}=="2340", MODE="0666", GROUP="plugdev"
# Texas Instruments UsbBoot
SUBSYSTEM=="usb", ATTR{idVendor}=="0451", MODE="0666", GROUP="plugdev"
# Toshiba
SUBSYSTEM=="usb", ATTR{idVendor}=="0930", MODE="0666", GROUP="plugdev"
# Wearners
SUBSYSTEM=="usb", ATTR{idVendor}=="05c6", MODE="0666", GROUP="plugdev"
# Wileyfox
SUBSYSTEM=="usb", ATTR{idVendor}=="2970", MODE="0666", GROUP="plugdev"
# XiaoMi
SUBSYSTEM=="usb", ATTR{idVendor}=="2717", MODE="0666", GROUP="plugdev"
# YU
SUBSYSTEM=="usb", ATTR{idVendor}=="1ebf", MODE="0666", GROUP="plugdev"
# Zebra
SUBSYSTEM=="usb", ATTR{idVendor}=="05e0", MODE="0666", GROUP="plugdev"
SUBSYSTEM=="usb", ATTR{idVendor}=="0451", MODE="0666", GROUP="plugdev"
# ZTE
SUBSYSTEM=="usb", ATTR{idVendor}=="19d2", MODE="0666", GROUP="plugdev"
# ZUK
SUBSYSTEM=="usb", ATTR{idVendor}=="2b4c", MODE="0666", GROUP="plugdev"
We need to download this file and to restart udev for the new rules to become operationnal.

Terminal
# sudo wget -O /etc/udev/rules.d/51-android.rules https://raw.githubusercontent.com/NicolasBernaerts/ubuntu-scripts/master/android/51-android.rules
# sudo chmod a+r /etc/udev/rules.d/51-android.rules
# sudo service udev restart