How to Look at Art-Formal Analysis

On the internet, there are an awful lot of videos explaining how to look at artwork. After searching and watching some of them, I have chose this Goya`s work entitled "The third of May 1808" .This video seems to me a good example to follow in order to depict artwork.
I consider it very useful to became acquainted with  terms such as texture, shades, symmetry  or  complementary colours.

 Since looking at art is not as easy as it could seem at first sight , that is my impression, some extra help is always welcome, I reckon.