To hell? From what I understand, it's the killing of living beings, and doing things that are based in anger. Of course I am not a Buddha and I do not actually have a deep insight into Kamma. I go simply from what has been written, and the killing of living beings is probably the one that is mentioned most, the intentional killing of living beings with the intention based in anger and hatred. Another one that's mentioned is the injuring of a Buddha or other enlightened people. We certainly wouldn't want to do that, so keeping one safe from anger and aversion is a very good way to try to keep from hell. It's good to develop compassion and lovingkindness and the ethic of non-harming.
I'll go further into what the Kamma Sutta says. The Buddha talks about the injuring of living beings, even if they're not killed, can get one to be reborn in hell. It's not automatic, though, hell entry, but one is born in an unhappy destination, or if one is reborn human, killing living beings will bring about a short life, and with injuring living beings, one is reborn with physical difficulties. If we look at our moment-to-moment mind-state we can understand this a little bit better. When we have anger in the mind usually there's a lot of burning in the mind, and we temporarily go into a state that is very, very difficult. We can't see clearly, the mind burns, we feel we want to destroy something. This is on a moment-to-moment level going to hell. So we would like to not be reborn in these hell states of mind but more in the divine states of mind.