this is one skill that takes time and practice. I used to have a 318i with a magnaflow muffler and for me that made a psychological difference becuz i could hear my engine better and adjust the revs that way. most of us know our cars by heart...
anyways, the 318ti pedals are just like the normal 318i. therefore here are my .02 cents. say your cruising down the road and start to hit some traffic. your in 4th gear around 2,500rpms. if you down shift to third the revs should put you around 3,500rpms(aproxx.) so what you want to do is match the rev. To do this put your braking foot near the right edge of the brake pedal. Use your heel as a pivoting device. You want to blip the throttle so with your outer edge of your foot just pivot it to the accel pedal and blip the throttle. JUst BLIP it. As your revs quickly climb to the desired level, this is the time to shift......so simply shift.
careful not to let the revs drop after you blip the throttle.
i dont recommend using big shoes.
ayrton senna called this technique "soel/soel"