Stencil camouflage design on the surface you're painting.
Paint the lightest shade first. Cover every part you do not wish to paint with the light shade in masking tape. Fill in the exposed area with the light shade and let it dry. After it dries, cover it in tape.
Remove the tape over the sections you're painting the darkest. Paint those areas the darkest shade of brown, let the paint dry, and then cover in tape.
Remove the tape from the patches you have not yet painted, paint them in the remaining shades of brown and let dry.
Remove all of the tape to reveal your camouflage design.