Approximately half of all punctured tyres can be repaired without sacrificing safety or expense.
The first thing you can do to help your chances of having a repairable tyre is to not drive on it once the puncture has happened. Putting on your spare tyre and driving to a repair centre immediately can vastly improve the chances of the puncture being repairable.
Punctures are also more likely to be repairable if the object was small, like a nail or screw, and if the punctured happened in the central tread (the blue section in the image to the left) and not the sidewall or edges (the red area).
British Standard has strict guidelines on tyre repair, but despite this, seeking out repair should always be your first choice, in order to save you the cost of a new tyre.