I will not give any hints to conversations, those choices are entirely your own.
Talk to everyone on the train, in order of distance that's Clem - Ben - Kenny - Chuck. Notice that Chuck would like a drink, and Kenny's very sad.
Go back to the wagon and pick up the bottle of alcohol. Go back to Chuck and give him the bottle.
Tell Kenny to have a drink with Chuck. Now you can reach the map bin, take the (Savannah) map.
Go back to Clementine. Talk to her about having a plan, train her in shooting, and cut her hair. After you've done all three, you'll move on to the next part of the chapter. (A hint with the shooting - you'll have to guide Clem's aim. When she shoots, look where the bullet hits, and guide her left/right and up/down accordingly. It's probably random, but I had to guide her right and up twice)
Talk to the people on the bridge. Climb up towards them, and talk to them.
Open the truck on the left. It contains road signs, and some tape - take the tape.
Look at the trailer that's hanging from the bridge, then climb back down for another conversation.
Walk towards the train station, and investigate.
On the right side, you'll notice a door. Look at the window above the door. Have Clem stand on your shoulders to check inside. The conversation should end in Clem reaching inside and unlocking the door.
Go inside, use the tool you still have to prop upen the door.
Notice the locked door, and the blowtorch behind it. Look at the gap above the door; Get Clem on the other side.
When the walkers approach you, walk backwards to the tool and pick it up; kill one of the walkers with it. (The second is a Quick-Time Event)
Talk to Clem, take the keys, open the gate and shoot the walker.
Pick up the blowtorch.
Go back to the top of the bridge. Use the blowtorch on the trailer hanging from the bridge.
Close the leaking hose by using the tape on it. (Gotten from the truck on the left, if you missed it)
Use the blowtorch on the trailer. The trailer will move, have Omar use the blowtorch while you hold him.
You have to jump onto the train, you can (but don't have to) kick the blowtorch down into the fuel first.
Last 'big' choice of the episode: Save Omar or Christa. Either way, the other one makes it onto the train by him-/herself.