during a game i find if i identify an area where i can score, and a shot that i can play to achieve it, then inevitably it will come off.
for example if a bowler is bowling quite full to me and mid on/mid off are in the ring, i'll think to myself that the drive back over the bowler's head is a safe shot. next time he over pitches, that shot will come out!
it's important to have a couple of shots in mind that you can play if the right ball comes along, rather than just reacting to the bowler.