I was practicing and I found out if I quickly let go of the clutch while applying gas everything is smooth. When I let go of the clutch slowly it is not smooth.

 

likei said, just drive and you'll understand everything we say. in bumper to bumper traffic, you are gonig to be riding the clutch (aka, releasing very slowly) rather than letting it go so in some cases that will be smoother.

on an open road, you'll want to release faster so you shift at the optimal rpms without letting them drop too much, so in this case releasing the clutch faster will be smoother.

just practice. ;)