Tournaments are one of the better ways unless you can provide a service (Head making, etc texture making,) You know, Supply something someone wants. l:U
[10:17][10:50] <diskimage> Where can I find the Toribash license?
2) Win tourneys - the promobot will advertise them every once in a while. Sometimes you don't even need any real skill to win them, just luck will do.
3) Make and sell art - textures, signatures, avatars, custom toribash menus, whatever. Make them and sell them.
http://forum.toribash.com/showthread.php?t=63013
http://forum.toribash.com/showthread.php?t=285
4) Of course win games in official servers, which gets you 10 TC per win.
5) Check out the events board, people make different competitions there - art, replays, etc. Sometimes it's just creative stuff. Prizes can be pretty big there.
http://forum.toribash.com/forumdisplay.php?f=37
I would consider all of those free.