Instructions since they added it to the repositories in 13.04+!

sudo apt-get update

sudo apt-get install nemo

Use the ones below if you want a slightly-more-up-to-date version.

DO NOT USE THESE IN 13.10, unless you aren't using a unity-based Ubuntu flavour.

To install the stable version of Nemo:

sudo add-apt-repository ppa:gwendal-lebihan-dev/cinnamon-stable

sudo apt-get update

sudo apt-get install nemo

To install the bleeding edge version:

sudo add-apt-repository ppa:gwendal-lebihan-dev/cinnamon-nightly

sudo apt-get update

sudo apt-get install nemo

Note: Nemo also shows up as Files in the dash, so the first instance of Files should hopefully be Nemo.

If you want to continue using Nautilus for drawing your desktop icons:

Show all the startup apps:

sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/nemo-autostart.desktop

Then, uncheck the item under Startup Applications that says:

Files

Start Nemo desktop at login