There are lots of ways to make Toricredits.
The most efficient and secure way I know of is selling Art. I have made 500k+ on my artwork, and I'm a lazy fuck. So, if you're active and really motivated to make art, do that.
Of course, as mentioned above there are other ways to earn Tc. Like duelling (effective if you're good in-game, just as Kristis133).
You also have marketing, were you basically buy cheap and sell expensive, not just items but artwork. The words "HQ", "Super", "Awesome" and "Legendary" have been used countless times, and supposedly add to the value of the texture/artwork.
You could also bet or use boosters (Ps. Never have a bet-off with Hampa, you'll lose).