The smash is the shot that the professional players hardly ever miss and that club players rarely get right.
The main reason for that is practice! - Club players hardly ever practise this shot.
It a hugely important one to practise though especially if you like to volley.
The moment you see the lob go up in the air you need to turn sideways - as if you were getting ready to serve.
As well as turning sideways bring your hands and racquet head up to around chest level with the same grip that you serve with.
Keep your eye firmly on the ball and start to adjust position so that the flight of the ball is in line with your body.
You also will probably need to start moving back, as you want the ball to come down just in front of you.
As you start to move you must stay sideways on, so use side steps and cross over steps to adjust your position.
As you start to get into position and the incoming lob is at its highest point you need to start getting your hands and racquet into position.
Try to feel both hands going up together - your non racquet hand should stretch up towards the ball, use your hand as an aid to track the incoming ball.
Your racquet hand should bring your racquet back behind you - into the same throwing position that you use half way through your service action.
Keep your head still and your eyes firmly focussed on the ball.
As the ball arrives throw the racquet head up to meet the ball as you would in a serve.
Don't try to hit too hard though - timing is the key.
The incoming ball will have plenty of pace on so a cleanly struck shot will generate more than enough pace to win you the point.