What I do to graph, is get a folder like used for reports, that has sliding spine to place over clear plastic front and back.
I take ruler, and make grid of 1 inch squares on one of them. I also do one in 1/2 inch squares on the next one. So I have two graphs to lay over a photo, depending on how big a photo I am working with.
Then very lightly on canvas or drawing paper, I take ruler and make grid there, I will either do those the next size up, or even bigger than the grid on plastic I am using over photo.
I sketch outline of subject, again lightly. And by comparing grid over photo to the drawn grid, I can make sure placement and angles are correct.
Also helps you when you can look and see something isn't right, as you can check with photo grid and look at canvas.
And by making permanent set on the plastic, you can use over and over, photos aren't ruined either.
Horses make me a better person.