I think the most helpful advice I ever got was to look at each shadow as a shape. ( this is kind of an abstract concept) but by that I mean sometimes our brains think too logically and stop us from seeing what's really there. ( ie, Brain: that is a lemon with a shadow, I already know what that looks like so I don't need to pay close attention.) also look at the colors of the shadows. We are preconditioned to think of shadows as gray or black, or just a darker shade of the predominant color, but often times they might seem blue or purple or brown, etc)
By now you're thinking I'm a nut, lol, but I guess for me, my biggest challenge was always turning off my brain's "know-it-all" attitude and seeing what is really there.
You're off to a great start by the way, a great sense of proportion. You've chosen a difficult subject with all the reds together but that will force you to make them more dimensional so that they don't all blend together.
Take an hour a day to work on it and study it. I'd love to see it in a week!