The truly advanced driver is one who exudes an air of quiet confidence who always has adequate time to make the correct decisions to deal with hazards and therefore make swift, smooth progress.

A major contributing factor to this smooth progress comes from limiting the amount by which the vehicle is unbalanced. When a vehicle is unbalanced it will transfer weight from front to back (squatting under acceleration) or back to front (nose diving under braking).
Avoiding harsh use of the accelerator and brakes will reduce the effect.

Changing gear offers an ideal opportunity to unbalance your vehicle by failing to "manage" or control the momentum in the engine.

So how do we manage this momentum when changing gear?
First we will consider changing "up" from, say, third to fourth gear.
Our first action when changing gear is to reduce the pressure on the accelerator, which will cause the engine to slow down.
If fourth gear is engaged by the time the engine speed has reduced by approx 750 rpm and the clutch pedal is released - then the engine speed will be close to that which is required to maintain about 40 MPH but in fourth gear.
The result is a good smooth gear change because we have not asked the rest of the vehicle to substantially alter the speed of the engine when the clutch was reengaged.

When changing "down" (from, say, fourth to third at 40 MPH) the natural tendency of the engine to reduce its speed during the gear selection process is no longer an advantage to us as the required engine speed in third gear must be higher than it was in fourth gear. lt is at his point that you will realise why
the system of car control demands that you finish braking before selecting the appropriate gear.
The reason is that (having completed all the braking) your right foot will be available to raise the engine speed (via the accelerator) while the clutch is disengaged to bring it up to about the speed that will be required when the clutch is re-engaged. This will avoid asking the vehicle to significantly alter the engine speed to match it to the road speed in the lower gear.
It sounds complicated but once perfected this technique has a lot to offer.

The alternative to using the technique as described - that practiced by the vast majority of drivers - is to release the clutch pedal slowly and therefore use the clutch mechanism as an infinitely variable secondary gearbox to disguise the fact that the engine speed is being dragged up, or down, to the required level while the road speed is being forced to meet it.

The other, equally unacceptable, alternative is to pretend the engine and road speeds are matched and put ones faith in the reserves of adhesion in modern tyres as the clutch pedal is released quickly. The result here is that the vehicle lurches down at the front.

By adopting an efficient (smooth) gear change technique as described it is possible to move unobtrusively from any gear to any other quickly without generating any unbalancing forces.

This means, for instance, that a gear change can be left until ALL available information has been given/received. The technique is also of particular use when you wish to select a lower gear for better flexibility. There is no intention to alter road speed but simply to engage a lower gear. You merely depress the clutch, and as the gear lever is moved from, say, fourth to third maintain the pressure on the accelerator to compensate for the increased load on the engine as it takes up the drive again. The whole manoeuvre is over in one or two seconds and the more flexible gear has been selected.