This is one of those frequently asked question. Sheldon Tapley answered it one way in the “Ask the Experts” section of Atlantic. He wrote,” You can’t – not without some serious effort.” That means, spend a lot of time looking at it and in particular those pieces that you just don’t get, - “a monkey could do that”. Try looking up close, from a distance, sideways. Then squint a little. Close your eyes, open them for a second and close them again and “see” what you remember. Leave the room and then come back in. Whew! If that’s not enough, ask the opinion of someone else but don’t interject yours (they know about monkeys too). Do some research about the artist, look at other pieces made during that period, listen to some of the music of the times . . . and now that you’ve earned a PhD in looking, you may still not know the answer, ”but you will be a more thoughtful viewer.” Thank you Sheldon Tapley! He is right, you know. If you want to learn something you have to spend time with it. Otherwise you are merely repeating yourself over and over and over. . .