Drawing on a large sheet of paper or on a wall is much different from drawing on a sketchbook page. The large expanse can make it hard to judge proportion, avoid smudges and create accurate strokes.
To get a better handle on drawing big pictures, you can use a number of steps to produce a great drawing.
In the beginning of your painting don’t get bogged down by details. Create the largest shapes of your subject using wide, sweeping strokes. Move your arm with each stroke, not just your wrist.
Draw Straight Lines
Forget the curves in a drawing. Only draw straight lines. Amazingly, this trick will help you draw your subject more accurately. As the drawing progresses the straight lines will disappear, leaving a well-drawn, large scale illustration.
Use a Maulstick
Once you get to smaller details it is important to avoid smudging your previous marks. Normally, putting a clean sheet of paper under your drawing hand would prevent smudging, but with bigger works you need something more substantial.
A traditional solution is using a maulstick stick. A maulstick is a rod that has a rounded tip on each end. You place the rounded ends on the edges of your paper and place your hand on the rod while you draw.
You can make a maulstick using these instructions: How to Make a Maulstick.
One of the best ways to check your proportions and composition is to step away from the drawing. Clip it to an easel or the back of a chair and step as far away from the drawing as possible.
The Upside Down Trick
Some artists like to check their composition and proportion by turning the drawing upside down. When an image is upside down the brain is more likely to notice mistakes or things that are out of place.