Practise Wall Training http://www.youtube.com/watch?v=mNiXrgAtjxc
Volley and half volley practice begins at 3:30
Devote at least some of your practice to hitting very tough volleys and half volleys of the type your opponent would hit. For this part of your wall practice expect to miss a few/shank a few. Getting used to pressure and how to handle tough volleys will allow you improve. Keep a few extra balls in your pocket for this part of the practice so you don't have to chase the ball after every miss.