Ubuntu 16.04 comes with Adwaita icon theme as the default one. If you want to make your Ubuntu 16.04 Gnome looks better, Numix Icon Theme Circle could be the best one available out there. Numix Icon Theme is a popular icon theme for Linux desktop. Personally, I have been using this Numix icon theme for many distributions.
This tutorial is going to show you how to install Numix Icon Theme Circle on Ubuntu 16.04 Gnome edition. Its pretty simple to install this icon theme since there is a PPA available for Ubuntu users.
Steps to install Numix Icon Theme on Ubuntu 16.04 Gnome
A. Add the PPA Repository
Open Terminal and paste these commands to install Numix PPA Repository on Ubuntu
sudo add-apt-repository ppa:numix/ppa
sudo apt-get update
sudo apt-get install numix-icon-theme-circle
B. Apply Numix Icon Theme
Open Gnome Tweak Tool and click Appearance. Then, select Numix Icon Theme Circle from the Icon list.
Now you should have Numix Icon Theme installed on Ubuntu 16.04. Thanks for reading.