
Originally Posted by
Battleship Pretension
Spelling and punctuation are essential. Typing speed should be respectable but doesn't have to be off the charts. The real keys are timing and readability. Captioning is not just typing what the person is saying. You also decide when the caption appears and disappears. Tying a new caption to a shot change or any sort of movement that indicates that a person is about to speak is a good idea. The idea is that the caption itself should work with the rest of the visuals and not be too distracting. Don't let any captions be too short or too long either. Right around two seconds a piece is a good rule of thumb. As far as readability, be wary of where you break a sentence if a caption is more than one line long. Again, the idea here is that the captions should flow.
Don't worry about when to use italics or when to move a caption to the left or right of the screen. Individual places have their own style rules and they'll teach you.