2 main formations really
Set Pieces: Gerrard/Aurelio/Alonso
Left Sided Attack
CB Overlap (Agger)
So, basically what we have is a core of Reina, Carragher, Alonso, Gerrard and Torres, who will play every game if fit (you can include Arbeloa there too). Rafa switched from 4-4-2 to 4-2-3-1 depending on the oppositions. Tough away games, and CL games, it will be 4-2-3-1. Home games against teams that park the bus, it will be 4-4-2.
CB rotates between Agger, Skrtel and Hyypia, depending on who's fit, and the opposition (against physical teams, Sami always plays). Aurelio is first choice LB, but Insua got a good run of games, when we was injured (which is very often), so both can be taken as first choice.
Talking about playing style, Liverpool game is about passing until they find a gap, and when defending, constant pressure and trying to win the ball back up field.
During build up, there are several passes between the CB, LBs and Alonso, who plays very deep to collect the ball. When he gets it, he tries to give the ball to Gerrard, as early as possible, otherwise, and plays it out wide to the wings.
Very little link up between Kuyt and Arbeloa on the right, and but Riera, and Insua/Aurelio is where attack comes from. When Gerrard has the ball, he always tries to find the killer ball to Torres/Keane very early.
When defending, the pressure starts from Keane/Torres/Kuyt who try to win the ball back. In midfield, Gerrard/Mascherano do most of the running, and Alonso tries to intercept passes. The wingers always track back.
When playing 4-4-2, Gerrard drop deeper, and Keane plays a supporting role. His game is about dropping deep to collect the ball, then either playing it back, or out wide. He always drifts wide in between games, making space for Gerrard to bomb forward. Alonso always likes to stay deep, but will take a shot from outside.