Motion with the pen in the air, tracing a line to the dot.
Put the pen on paper and draw the line.
Repeat from different angles.
If you draw lines at different angles, you will notice that you are naturally better at placing lines in a certain direction. You can always rotate the page, but if you do this exercise, you become better at drawing a straight line from any angle and you won’t need to break your concentration rotating the page.
Grab a pen or pencil and some paper, and start drawing!