Blast Effect

Start out by resetting all brushes, and going to a nice star brush, like below.

Go to the Brushes dropdown, turn on Scattering, and, well, make the settings look like below.

Create a new layer, and draw some stars in it. Change the size alternately to make it look better.

Make another layer, take the scattering off, and draw a few really bright stars by repeatedly clicking in one spot.

With your newest layer selected, go to Filters, Blur, Radial Blur.
Make your settings like below.

...which will make this...

Go to the Lasso selection tool, set the feather to 20 px, and make a selection like below.
Make sure its neck reaches all the way to the upper left-hand corner.

Go to Radial blur, but this time check Zoom.

Next go to the Blur tool, set its mode to Lighten, and with a big brush, blur the blast.
It's the easiest way I know of to make the particles brighter.

Using the feathered Lasso selection tool, select some more stars, and repeat the whole process, only this time with a little less zoom intensity.

Now you play around with the whole thing until you like it.

Create a new layer, set its Blending Mode to Color, and with a Paint brush set at very, very low opacity, slightly color the source of the blast.

You're done!