"I am told that a common mistake among the not so good is. Not going to the end of the step. Which results in a shorter step than it should be. Also turning into a step and again not turning at the end of. Has anybody else been told about this mistake."
Yes. But to really understand it, you have to speak specifically about what is supposed to go straight, and what is supposed to turn.
We have to answer the question for each part of the body, and there are actually two questions: in what direction should it move, and in what direction should it be oriented? The answers won't even be quite the same for forward and backwards movements, nor ultimately for right-turning and left-turning movements.
So let's gown down to details.
When your teacher tells you to move straight forward and not turn until the end of the step (actually, in many cases not until late in the SECOND step), they should be speaking literally about the DIRECTION OF MOVEMENT. Whatever direction you start the figure moving in is whatever you keep, usually for two entire steps.
But many turning figures use Contra Body Movement (CBM), which is to say rotation of the body, during the first step. What this means is that even as the body moves in a straight, unchanged path, it also rotates during the course of the movement, while not letting this rotation change the direction in which it is travelling.
And then we speak of the direction of the feet. In forwards actions, it is customery for the feet to point essentially in the direction of movement. So you would take two forwards steps with the feet pointed in that direction, and then late in the second step you would rotate both feet to account for the change in the body orientation.
In backwards actions though it is usually different. Customarily, even as the foot swings straight backwards, it will rotate some so that it lands in a position consistent with straight movement, but toed in a bit. This greatly eases the next part of the turn. The second step of a backward turning action usually points the foot in the new direction - what we call a pointing alignment.
As you can see, there are a bunch of details to learn. But the important questions on the subject of turn are
1) Are we talking about direction of movement, or direction of orientation?
2) Which body parts specifically are we talking about?
