For an average speed twist serve I actually just stand back and let it drop. As someone said you should be taking a good crack at the ball if you do this because your court position won't be the best.
However, for bigger twist serves, I feel you have to take it early. I basically just use volley- like technique like Lee mentioned with a very short backswing. I find it hard to consistently hit an aggressive return off that serve, I'll often miss-time the ball
A lot depends on your return style though . Not everybody likes slicing/chipping their returns