I think it comes down to the intention of how we want to affect others. I think an evil act is one done out of the intention to cause suffering (for the sake of suffering). I think it's harder to describe what makes an act good, but it seems to involve the intention of making things better, as vague as it sounds.

It's also important to pay attention to the consequences of actions too. Although we should differentiate between good/evil actions and good/evil people.

What're your thoughts on the matter?