Install the GPG key:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 1F3045A5DF7587C3
Ensure apt is set up to work with https sources:
sudo apt-get install apt-transport-https
Add Skype APT repository
echo "deb [arch=amd64] https://repo.skype.com/deb stable main" | sudo tee /etc/apt/sources.list.d/skype-stable.list
Update apt sources and install Skype for Linux
sudo apt-get update
sudo apt-get install skypeforlinux