Before you trace a single edge, find the horizon line. It is the most underused tool in reference-based drawing, and it solves placement problems that hours of careful outline work cannot fix. The horizon line is simply your eye level in the scene. Everything above it sits higher than you; everything below it sits lower. Get that line right and the rest of the drawing has somewhere to belong.
It is not the edge of the land or the top of the sea. It is a horizontal line at the exact height of your eyes when the photo was taken or the scene was observed. Tilt the camera up and the horizon drops in the frame. Crouch down and it rises. In any reference, there is one and only one true horizon line, and it runs perfectly level across the image.
If you are working from a photo taken with a tilted camera, the horizon line is still level in the world, but it appears tilted in the frame. That is a warning sign. Tilted horizons distort every vertical and make accurate tracing much harder. When you can, shoot or choose references with a level camera.
You do not need a ruler and a spirit level. You need three checks.
Mark that line lightly across your reference. Everything you place afterward gets measured against it.
Once the horizon is marked, scale becomes a calculation instead of a guess. A figure standing on the ground has feet below the horizon and head somewhere near it, depending on their height relative to yours. Two people of the same height standing at different distances will both have their heads on a line that converges toward the horizon. This is why crowds in old paintings look correct and crowds in beginner drawings look like stickers pasted at random.
Trace the horizon first, then trace the ground contacts of every object, then build upward. The feet, wheels, and bases tell you where things sit. The horizon tells you how big they should be.
If your drawing feels floaty or wrong and you cannot say why, check the horizon before you redraw a single contour.
Ask yourself one question about every reference: where was the camera? At chest height, at eye height, on the ground, up a ladder? The answer tells you what you are looking up at and what you are looking down on. A cup on a table looks completely different from eye level than from above. Tracing the rim without knowing your eye level is how ellipse drawings go wrong.
When I am working from a phone overlay, I mark the horizon on the reference layer before anything else. It takes ten seconds and saves the whole drawing. Tools like EchoDraw make this easy because you can hold the reference in place over your paper and see both the live scene and the guide line at once, but a pencil line on a printout does the same job.
Plenty of references have no visible horizon: a close-up of a face, a still life on a table, a detail of a hand. The horizon still exists, just outside the frame. You can often infer it from any receding edge, from the tilt of a cylinder's ellipse, or from the direction a shadow falls. If you truly cannot find it, choose a plausible eye level and stay consistent with it. Inconsistent eye level is what makes a still life look assembled from parts.
Take five references and do nothing but mark the horizon line on each. No drawing. Just the line, plus a note about the camera height. Then take one of them and trace only the ground contacts and the horizon, nothing else. You will be surprised how much of the composition is already decided. Do this for a week and you will start seeing the horizon automatically in every scene you look at, which is the actual goal.
Grab EchoDraw and turn any photo into a live tracing guide.