Darryl, a survivor and michonne are in an abandoned town, we can tell from the way they are just out in the open that its not swarming with zombies. The three then go in the store which leads me to assume that Rick has sent out them as a party to search towns for supplies
Next scene we see sasha instructing a group larger than the previous one, that has darryl, tyrese, glenn, michonne and what I can assume to be, the survivor from before in the first segment(survivor #1, whose face is not seen)
Next scene we see Bob Stookey, a new character (read his page for more info) who is seen guarding the front of the store, we then hear a scream (a character may have been bitten) I am assuming this character is most likely survivor #1, because he is most likely a red shirt, Bob stookey then rushes in to investigate.
in the second segment, we see an overview of the prison land, there appears to be wooden sheds and garden patches, just like what was proposed in the first ep of S3. there is also a large number of zombies on one corner of the fences
we see then:
Darryl out surveying the area with carol
carol then goes on to say that the zombies don't spread out anymore (highly likely a section of fence will be taken down) she mentions walkers going towards tower 3 (meaning the are most likely utilising more and more of the prison and are becoming more organised, to the point were the group is numbering the towers. as she is speaking we can see:
an inordinate amount of zombies have arrived at the prison, the woodbury citizens and Karen are killing zombies at the fences, michonne using a horse (they may now have horses on hand) and one of morgans traps making an appearence meaning rick liked morgans ideas of traps and is using the design of them.
carol states that the problem is managable but if the group cant get ahead of it, not for long
at 0:57 we see there is a woman on the guard tower, meaning the group is now using the watch towers
we hear a scream, that is played over a shot of rick and carl in a veggie patch and a reaction shot of the guard tower woman. (the scream sounds like its in an enclosed area, like its coming from within the prison, the echo of it. which leads me to think there may be 2 problems, the scream from the prison and the one that matches from the reaction shots of rick, carl and the watchtower survivor
at 0:59 we see a balding, man who is aged between 40-60 who is aiming a shot gun at someone in the prison, he then shoots the shot gun 1:00 - that concludes the first minute, I will be covering the rest of the trailer shortly, add what ever you can in the comments if I missed something