Depends on what keyboard you are using. On the stock Sony one there are two arrows in the bottom row next to the return and they will move the cursor left or right.
On the Android keyboard there isn't a way, you just have to randomly poke at the screen with your finger until you get to the right place or give up, get near enough and just use the backspace delete until you can correct your typing.
There are other keyboards on the market that you could try that may have different functionality.
