Continuity Editing

180 Degree Rule
This keeps the camera on one side of the action and is usually used to view 2 characters during conversation as it keeps the focus on the characters and allows the expansion of the frame into the unseen space off-screen. It is commonly described as a rule because the camera is not allowed to cross the axis of action otherwise it may give the impression that the actors positions have been reversed.

Match On Action
Here we see a piece of action and then we see where that action came from. It's a cut from one shot to another where the second shot matches the first's action. This is used to keep the flow of scene going as it links the shots together and gives the impression of continuous time.

Shot Reverse Shot
This is used most commonly during conversations as it shows a shot of one character looking towards another character but then cuts to a shot of the other character looking back at the first. This can be used to show the audience what a character is looking at or (as I said) to show a conversation. 
In the images below it also shows the 180 degree rule which isn't broken until Guy Pearce (Aldrich Killian, the red lava-man) is hit by a pole.