The mistake with many amateurs is to use the same amount of screw, side, or top for all strokes and to vary the force of the stroke.
The reason why this is a mistake is that position can be much better preserved by grading the cue contact.
A few illustrations of this may be usefully given.
The object ball is so near to the cue ball that central striking will overdo the stroke, whilst a finer than half-ball stroke will send the object ball in a wrong direction.
In such a case a little "top" will put so much way on the cue ball that the half-ball stroke can still be made and position preserved.
In another case exactly the reverse conditions prevail. A half-ball near stroke would not cause the cue ball to deflect quite enough and yet the half-ball stroke is desirable.
Obviously, the thing to do here is to strike a shade below the centre of the cue ball and to make the stroke perfectly while retaining position.
In a third instance, the relation of the cue to the object ball might be as described and the necessity for half-ball contact the same, but the cue ball might have to strike a cushion before reaching the second object ball and would just miss it on the inside.
It is clear here that a slight amount of running side on the cue ball will enable all the necessary conditions of the position to be fulfilled.
To the proficient billiardist most of the foregoing will appear to be too trivial to be printed, but that is not so.