Abigail acts selfishly almost exclusively. I can't think of anything that she does that isn't selfish. First of all, she lies about what was going on in the forest. As Betty reveals, it wasn't just dancing that was happening, but Abby "drank a charm to kill Goody Proctor." Abby lied about this to Parris, and then threatens the girls about telling anyone about what happened. The charm drinking in the first place was selfish--she wanted to kill off Elizabeth to be with John, a definitely selfish move. Then, to hide that selfish act, she threatens the girls and lies aobut it to Parris. Lying about it, and threatening the girls serves only to protect her own skin, AND leads to all of the girls accusing others of witchcraft so that they won't get in trouble. Those accusations lead to the direct downfall and death of many people.
Abby continues to act selfishly every time she makes an accusation, because it gives her power and attention, and keeps her secrets hidden, and each accusation that is made harms another person. Her "needle in the belly" incident was selfish--it was just a way to get Elizabeth arrested so that she could be with John. That led to Elizabeth's arrest, and indirectly, later on, to John's arrest. Her actions in court in act three are all selfish. She leads the girls in pretending Mary Warren is a witch--she does this to protect her name, because Mary is about to oust all of them as liars. Her accusation of Mary is selfishly trying to protect her own reputation in the courts and town. Accusing Mary leads to John's arrest. Then, in the end, when Abby steals her uncle's money and bails town, that is selfish because she realizes the town hates her and will turn on her. So, she ruins her uncle's wealth and reputation by leaving town with his money.
From the moment Abby enters the scene, she acts entirely in selfish ways, to the tune of destroying many, many lives. I hope that helps; good luck!