Your eye can play tricks on you! Here is a tip to help you to position the major lines of your subject following the rules of proportion.
After drawing an item on the paper, take the time to back up a few steps. Make sure there is overall consistency and the proportions have been respected. Then go back to your drawing.
Remove the middle from a cardboard rectangle to form a frame. The removed part should be the same size as the sheet of paper you are going to draw on.
Attach pieces of string with adhesive tape from one side of the frame to the other every 2 centimeters (both height-wise and widthwise) to create a grid. Make sure the strings are quite parallel.
Place your frame in a convenient place in front of the subject you want to draw. The closer you approach the frame to the object, the tighter the angle.
Create a grid on your sheet of paper by drawing vertical and horizontal lines every 2 centimeters. Do not press down too hard on your pencil because you will need to erase those later.
On your sheet of paper, draw what you see in the frame, square by square.
Once you have sketched out the lines of your drawing, you can gently erase the grid.
Use a mirror to check the accuracy of your drawing. Identifying construction and proportion errors is faster with a reflected image.