There are many ways of downshifting gears
best way of downshifting is to release clutch when gear shifted from like example 5th to 4th and

Press clutch - down shift - release clutch (at same speed when you left it at the time of upshifting..)

DON'T DO:

don't shift gears while Pressing clutch all the time...this will make you engine free and effects in your breaking...
downshift should be directly-proportional to the RPM....RPM should not go down while downshifting gear...

Use of Clutch....

The main and most important use of clutch is to reduce jerk while changing gear with out clutch chain set life would be very less and engine would be rough...

So use your bike clutch precisely