Poli Poli Approach

  When your composing your picture, locate the center and sides of the image.  Position the painting directly under the image you are going to paint.  Position yourself the correct distance away from the support (painting) so the sides of the support mark the sides of the image in front of you. 

Draw a center line on the support and mark three obvious relation points from the image on the support.  These position marks can be any distance away from you and one of them should be on the center line.  If you can see the horizon line draw it in, if not draw in a horizontal center line.
I use a second set of three markers using one of the first sets' marks. This gives added accuracy. All of this is very important for figures and landscapes.

This is a very old image, 1980, back when the rode was dirt, computers were 1.8 gigs and jpg was in style. Today I have 20 gigs in my backup drive. 2015, Update again, my backup Time Machine is 2 TB. I wish I had used the full setting of the jpg, today I use png.