I'm actually tired of seeing the regeneration. Hold a couple of Matt Smith episodes in reserve and just start airing the next Doctor's episodes without any explanation. Hit the ground running with a new Doctor and a new companion and none of the usual Regeneration tropes.
Then, air one of the Smith episodes. Maybe it has a few teases about Eleven facing something big.
Then, back to Twelve.
Keep going like this for at least a year. This keeps the formula fresh, the audiences buzzing, and the Doctor's age unknown.
Then reveal we haven't been watching Twelve at all. It was the Thirteenth Doctor!