A simple trick that creates a huge difference when drawing lines is to look at the destination when drawing
Travelling with a pencil from A to B; focus on B and not on the pencil or drawing the line
A momentary glance is all you need, or, you may find resting your eyes at point “B” works better for you.
With practice, it helps you keep a steady and straight line.
The technique is useful when drawing lines that you wish to look straight yet without the rigidity of using a rule.