Dead blockers slow the ball down (throwing off your timing), and keep it shorter than you are used to. To compensate, serve and rally as deep as you can. This makes it difficult for the dead blocker to deaden the ball, and it gives you time to adjust your timing to their dead balls. It also gives you time to get your best shot into play. Put lots of spin on the ball (topspin and backspin, but sometimes even sidespin loops) to force errors, and be ready to follow up with winners.