First go to the Dropbox website and download the .deb package. Make sure you select the (x86) package.
Once the download is complete, double-click on it to start installation. When the installation is over you will need to restart Nautilus; you can do this by logging out and back in or by executing the following command in Terminal (Applications -> Accessories -> Terminal).
Now you will see the Dropbox icon appear in the taskbar.
Right-click on the icon and select “Start Dropbox”. This starts the downloading of Dropbox. Sit back and wait until the download is complete.