ssh -i ~/.ssh/id_rsa -D 1337 -f -C -q -N sammy@your_domain
Explanation of arguments
-i: The path to the SSH key to be used to connect to the host
-D: Tells SSH that we want a SOCKS tunnel on the specified port number (you can choose a number between 1025 and 65536)
-f: Forks the process to the background