Your results letter will identify the topics in which the mistakes were made. It makes sense to target these for extra learning before you retake the test.
Ask your driving instructor how you should best proceed. It may be a good idea to try a new learning tool, such as a book or CDROM, to give you fresh insight into the theory of driving. Just going over the same stuff as you did before can be very tedious!

You only have to wait 3 working days after failing the test before you can take it again.
However, if you failed because you really weren't ready for the test, then you would be wasting your money to apply again immediately without doing a lot more preparation.