First off, It's easier if we get a piece to work around, or if you want, just start off with a:

1. 500x500 canvas with a black background, like so: Preview

2. Select your brush tool (B)

3. Click on 'Windows > Brushes'. A new window should popup, like this: Preview Click 'Brush tip shape' and find the 'Star 33 pixels' brush. Preview Now follow these settings: Brush Tip Shape Spacing: 50% Shape Dynamics Size Jitter: 100% Scattering Make sure 'Both Axes' is ticked. Scatter: 436% Count: 4 Count Jitter: 21%

THERE ARE MY PERSONAL DEFAULT SETTINGS, FEEL FREE TO PLAY WITH THESE SETTINGS TO ACHIEVE YOUR OWN DESIRED EFFECT!

Now go back to your canvas, make a new layer and start drawring your stars. (make sure your foreground color is white) Preview

Now this is nice, but give this star layer an outer glow, with an opacity of 50%! (right click layer and go to blending options) so now after a few mess arounds, the outcome should be like this: Preview

For a better piece where this star dust is used, check this: Preview