Go underground. Steer clear of natural caves.
Seriously, he's a joke underground. Can't fly above you. Learned that one the hard way.

5209204 Try that... On a modded sky block world. That's the place I've had the biggest trouble with the Wither. It ended up literally destroying my entire world, and I had to restart the game because I couldn't kill the thing...

However, it always seems to do way too much damage to me. How do you avoid being hit? And sword, or bow for attacking it?

5209218 I recommend one Notch Apple and one Diamond Sword. Full set of iron or diamond armor never hurts, either.

5209626 I can do that, just a bit more prep there than I usually do. Thanks!