The Gunners are 2-1 down after a largely poor performance in Spain, and must win the home leg 1-0 or by two clear goals to go through to the semis.
Arteta was asked what his team must do differently, compared to their display last Thursday.
During a press conference, he told reporters: "Well, the way we started the game that's for sure.
"We did some things that we didn't talk about. We conceded an early goal that I think was difficult to swallow. It took us a little while to react and I think we had a difficult period.
"How we handled both boxes. And the discipline. To play with 11 players in this competition is key and we didn't manage to do that.
"When we do all the things that we have to do the game will be completely different."