1994 Vauxhall Cavalier Emision,s for MOT

hI, MY mot IS COMING UP SOON, LAST YEAR MY EMISSION,S WERE A NIGHT MARE. I have turned down the fuel screw, lack of power but got passed the test. I wastold to clean the fuel system out. What is the best way of doin this? I was told to thrash the car for a few miles. Is there any GOOD aditive i can put in to the tank, to get the emission,s down. I know its an old car, but it,s a gud un. Every thing else is ok. Thank you Paul