Explosion Effect

Step 1: Open a new file. 680x510 pixels, 72dpi.

Press D to set the background color white and front color black.

Step 2: Filter > Render > render > Clouds.

Step 3: Filter > Stylize > Find Edges

Result:

Step 4: Ctrl + L to change the Levels. Select Auto. Result:

Step 5: Use Air brush tool paint like the picture below. (As cloud)

Step 6: Use Magic Wand Tool selects the black part.

Step 7: Select Inverse.

Step 8: Shift + Ctrl + X to open the class=Spell>Liquify window.

Click to enlarge

Step 9: Use Pucker Tool & Bload tool to do draw some bubble and concave.

Result like the picture below.

Click to enlarge

Step 10: Ctrl + D to Deselect.

Step 11: Image > Adjustments > Gradient Map.

Step 12: Click on the color bar to edit the Gradient Map as following.

Black > Brown > Yellow > White

Step 13: In the end, use Dodge tool, Burn tool, Blur tool and Smudge tool to make the work better.