Key tactic: Both sides have played 4-2-3-1 formations in their opening two fixtures. I think the key tactic here might just be how the two sets of holding midfielders cope with their defensive responsibilities. From the sounds of things Jordan Henderson will be out for Liverpool with a foot injury. This could be a good thing for Brendan Rodgers' side. It likely means Emre Can will partner James Milner at the base of midfield. I'm not convinced the Henderson-Milner partnership is a great one. They are similar players in that both are more all-action box-to-box types than calming, assured figures in the middle of midfield. Double pivots tend to work better when there's an obvious deeper lying midfielder partnered with one that performs the box to box role (in other words there's not much actual pivoting between the two). I think Can will offer tactical discipline in front of the back four and provide a platform for Milner to drive forward and help in the attack. Arsenal tend to overload the middle of the pitch in attack so Milner and Can will have to remain disciplined.
For Arsenal, Francis Coquelin could be given a decent test by Adam Lallana and Coutinho. The two have consistently rotated between the #10 and a slighter wider role in Liverpool's opening two matches with Jordan Ibe maintaining a wider position on the opposite flank. Lallana and Coutinho will look to combine in the spaces between Arsenal's defensive and midfield lines. Coquelin will have to be conscious of their movement. He played well overall last week but committed a couple of fouls after already being booked and was perhaps lucky to not get sent off. (He committed 4 fouls which is a lot but how often do we see Fernandinho commit 4 fouls over the course of a game to cynically break up opposition counter attacks without anyone calling for him to be sent off?)
It's also probably worth pointing that Arsenal need to do a better job of closing down the opposition when they get into shooting positions around the 18 yard box. In both of the Gunner's opening fixtures they were guilty of not committing themselves to get blocks on opposition shots that resulted in goals. In Coutinho, Liverpool have a player that has proven he's capable of scoring magical goals from outside the area. He won't hesitate to have a go if he isn't closed down.
Key stat: I'm not sure how "key" this stat is to Monday's game but it highlights the difficulties Liverpool have had in their visits to the Emirates: the Reds have won just once at the Emirates since it opened in 2006. That win came after Emanuel Frimpong was sent off in the second half, followed shortly after by an Aaron Ramsey own goal. Luis Suarez sealed the points late on.
Liverpool were battered 4-1 at the Emirates last season in a match where they had a golden chance to go ahead early but failed to convert. They'll need to take advantage of any opportunities that come their way Monday evening to take anything from this one.