A. If the ball is hit at your upper body (chest or head):
Slide to the left (not backwards) with your left foot and hit the approaching ball with the forehand side of the racquet. Slide to the right (not backwards) with your right foot and hit the approaching ball with the backhand side of the racquet.
In both cases, try to keep the racquet head up. These side steps help you clear your head out of the path of the approaching ball. The backward step results in the racquet flying backward causing mis-hits.
B. If the ball is hit at your lower body:
No need to side step or step at all. This ball requires you to drop the racquet head down (breaking the traditional ready position or racquet head up position). It is to your advantage to hit these balls with the backhand side of the racquet for ease and quickness.
Typically, on a normal volley, you would like to go after the ball. But, in this scenario, try to bring your racquet back to your body from ready position. This will allow the ball to come into your motionless racquet and avoid the common mistakes of swinging instead of BLOCKING - BLOCKING is the key!