It really depends on the shape of the plane. But as a rough rule of thumb (and I do mean rough), you can take the very forward leading wing edge (this could be the tip of the nose on a wing) and measure back about 28%-33% and start there.
I replied earlier but for some reason (my fault no doubt) the post didnt show up. For a 'true' triangular delta wing with no tail then a good CG is around 45% root chord. For other shapes here is a calculator: Flying wing CG calculator