When I am told something like this by one of my teachers it usually means I am not seeing things the same way (s)he does.
Find a painting in a similar style that you are trying to emulate (expressive realism, cubism, etc)
Study everything you can find in that style, and put them side by side (thank goodness for computers!) with your work.
Study them closely.
Go to a real art museum and view them as close as you can (until the security guards start yelling! No I did not mean to actually touch them..). Ask for comments from others in the class. (NO- do not ask Mom).
Take a photo of your work.
Post it on line for others to C&C.
Look at it from a far distance. (no, you didn't need to go THAT far, now get back in the room)
hang it upside down.
Squint. take your glasses off.
Look at it in the shade outdoors,
under fluorescent light,
under 'ideal' lights,
hang it in that awful green dining room (what were you thinking?)
In other words, look at it so many times it begins to become an object and not YOUR painting. Then you will begin to become objective.
If you still like it, very good.
If you still love it, congratulations.
but chances are, you will become more objective in the process.
That was what the instructor was looking for.
life is good