As much as an explosion in the sky might be really cool to watch, it probably isn’t the safest to have unpredictable bits of rock raining down on everyone…so I’d probably opt for somehow trying to nudge it on to a difference course. How I’d go about this, I don’t know. Luckily, astrophysicist Neil deGrasse Tyson does – and you can read an interview where he talks about it here: http://globalpublicsquare.blogs.cnn.com/2013/03/01/how-we-could-stop-a-meteor-hitting-earth/.
It would all depend on the size and the make up of the asteroid that was coming to earth. If was small then it would burn up it the atmosphere but it was tens of kilometres wide then we would have to try and deflect it from its path.
I am not actually sure how this might be done but Bruce Willis in Armageddon managed to do it so maybe we should send him up into space if there is ever this threat :).