Just because I've installed it so many times now, I figured it'd be a good idea to have all the steps in one place where I can easily c/p. This assumes an Ubuntu 16.04 variant.
sudo apt update ; sudo apt upgrade -y ; sudo apt install git python python-pip ssh tmux htop -y
sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
sudo apt-add-repository 'deb https://apt.dockerproject.org/repo ubuntu-xenial main' ; sudo apt update
sudo apt-get install -y docker-engine ; sudo usermod -aG docker $(whoami) ; sudo reboot
pip install --upgrade pip ; sudo pip install docker-compose
git clone https://github.com/OpenDroneMap/WebODM --config core.autocrlf=input
cd WebODM ; ./webodm.sh start