Snow Globe
There is many ways to do this trick. I normally use the Layer Filters but the tutorial doesn't to make it compatible with more programs.
You will find the basic trick for the highlights and shadows, but feel free to add more.

1. Start with a basic circle shape . Hold shift for a perfect circle. Make sure it's centered.

Never Delete or modify this Layer... always make a duplicate first.

2. Paste your image

The Front Highlight.
3. On a new layer , create a small circle.

4. Hold CTRL and Click on this Layer on the Layers Menu. Animated example

5. Hold ALT and Press the Down arrow several times.

6. Feather (CTRL+ALT+D) your selection and hit Delete.

The Front Shade.
7. Make a duplicate of the original circle.

8. Hold CTRL and Click on this Layer on the Layers Menu. Animated example

9. >Select>Modify>Contract. choose a large value (100 or more depending on the resolution of your image).

10. Feather (CTRL+ALT+D) your selection and hit Delete.

The Back Shadow
11. Create a small circle on a background layer.

12. Choose >Filter>Blur>Gaussian Blur to soften the edges of this one.

The Lens Flare
13. Once again, Create a duplicate of your original circle.

14. >Edit>Fill> Content use: 50% gray.

15. Apply >Filter>Render>Lens Flare.

16. Apply >Filter>Distort>Spherize (choose a value of 100%)

17. Change the Layer Mode to Overlay.

18. Add a background or paste the whole thing on your layout.

19. Modify the opacity of each layer.

20. Create the base for your wonderful snowglobe.

You can do the snow flakes just like the Starbrush; simply add a Roundness Jitter to give the flakes a 3D look.