Finally, here goes real Photoshop trick! The soft brushes are good for background colors, and hard brushes are good for outlines, but neither are good enough to draw fire. I tried using my tablet pressing hard brush gently, but I ended up with dragon made of fur, not fire :-) So I started playing with changing settings of default Photoshop brushes. Finally, I achieved something that satisfied me (I realize it is not perfect but drawing fire takes a lot of skills, I am only starting my way to it). You can download tool preset and try this brush yourself. DOWNLOAD TOOL PRESET.
 
Fire Dragon - making of - Step 12

Using this brush, make some strokes around the edges of dragon... (on this image, I show only this layer on black background, so you can better see how this brush looks)
 
Fire Dragon - making of - Step 13

And then set layer mode to Overlay, and duplicate layer. This is the result, shown with all layers visible.
 
Fire Dragon - making of - Step 14

Next trick is usually used in tutorials like Make your own Aqua OSX wallpaper! But I found I wanted this effect here too. Set color to grey (HEX 808080). With pen tool, create a shape of dragon.
 
Fire Dragon - making of - Step 15

Set layer mode to Overlay. Because layer is grey, it will become invisible - do not worry! :-) Create new layer, and with black and white large soft brushes, put some dots here and there.
 
Fire Dragon - making of - Step 16

Then, Create clipping mask (from layer menu). Magically, the brush is masked by vector layer, and inherited overlay!
 
Fire Dragon - making of - Step 17

You can repeat the same steps to create additional curve inside wings.
 
Fire Dragon - making of - Step 18

And, use the same technique to make dragon head (or, unlike me, you could do it on previous step! That would be wiser :-)
 
Fire Dragon - making of - Step 19

This is how the head looks when I set shape layer mode to Overlay, then add black and white brush dots, and create clipping mask.
 
Fire Dragon - making of - Step 20

Use Pen tool to add white eye, then set its layer mode to Overlay too.
 
Fire Dragon - making of - Step 21