There are different ways to earn toricredits.
1) Buy toricredits and boosters - it costs real life money, but is the most effective way. You also get a lot of free promo items that you can use.
http://forum.toribash.com/showthread.php?t=78515
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
Well some ways are
Just playing the game/being good.
Creating and selling textures for people
Creating and selling signatures/avatars for people.
Which is done here: http://forum.toribash.com/forumdisplay.php?f=371
Or doing surveys and stuff located here: http://forum.toribash.com/tori_survey.php
Another final option is buying toricredits via paypal or some other payment method available on the page http://forum.toribash.com/tori_depositcredits.php
Hope that helps.