It is difficult to really guage the problem without actually seeing you in action, but I would have to say anyway that you should practice drawing with the shoulder and elbow rather than the wrist.
Most people like to rest their arm on the table when they draw and move the wrist, which gives a short, curved stroke. However, if you elevate the arm to let it move and keep the wrist locked, the shoulder and elbow in combination can provide a fairly long, straight movement at the pencil point.
Also, don't be afraid to draw a line more than once. When you put down a line, if it is not to your liking, leave it there while you draw another one. The combination of looking at the incorrect line as a guide along with the repetition of the movement will eventually lead you to put down the correct line, at which point you can erase the bad ones.
As the ego shrinks, so the spirit expands.