I don't know if you appreciate comments or not, but my advice -

1. Make the borders dark, and add a light source

2. Blur the background a bit...(very tiny bit)

3. If you're using Photoshop, make a new layer and apply image and then go to Filter->Other->High Pass and set it to soft light.
But if you're using Gimp, then there must an alternative to it, so do that.


If you follow my comment, then please post the improved version, and if possible, post some of your older works so we can see which weakness is common to them and suggest you to focus more on it.