Top: Original painting "Tulip" by Derek John (see my comments in the Flower Portrait Painting Project Gallery).
Middle and Bottom: My suggested changes. I would be tempted to crop the left-hand section of the painting so the curtain goes off the edge of the composition. This removes the small bit of wall to the left of the curtain which I find very distracting, and shifts the vase more towards the left-hand third of the composition (Rule of Thirds).
I would also be tempted to crop off some of the right-hand section of the painting (as shown in the bottom photo) to help the vase and flower dominate the composition. This will also reduce the feeling of the painting being divided into two halves (the "full" left-hand half with the curtain, vase, and flower vs the "empty" right-hand half).
Middle and Bottom: My suggested changes. I would be tempted to crop the left-hand section of the painting so the curtain goes off the edge of the composition. This removes the small bit of wall to the left of the curtain which I find very distracting, and shifts the vase more towards the left-hand third of the composition (Rule of Thirds).
I would also be tempted to crop off some of the right-hand section of the painting (as shown in the bottom photo) to help the vase and flower dominate the composition. This will also reduce the feeling of the painting being divided into two halves (the "full" left-hand half with the curtain, vase, and flower vs the "empty" right-hand half).