Then maybe your problem is that you try to cram too much into your piece from the start.

I don't know about the professional professionals, but I'd generally think that if you have too many themes in your story to condense into a 2 page short short, then you probably have too many themes for a 500 page novel.

But then, my writing is very simple, and more entertaining than deep and intellectual. Again, I don't do poetry. I don't write about dead babies.

I'll agree that practice is the best you can do. Every day. Every night. Keep a little notepad to jot down ideas and revelations and brainstorms while you're shovelling mud out of a giant hole in the ground (or whatever it is that you do)...