OK here's a sticky little thread for you to go to as a reference:
1) Go to
http://www.ninjam.com/farm-status.php to see a list of servers, and if anybody is jamming on them.
2) If nobody is jamming, go to the first server in the list ( test.ninjam.com:2049 ) and go there and play and wait. Someone will join eventually! Usually it doesn't take too long!
Repeat.
-Justin