Here goes most fun and time-consuming part: outlines. For next steps below, I made outlines with small hard white brush, then set layer mode to Overlay.
 
Fire Dragon - making of - Step 22

This is how it looks with layer mode = overlay...
 
Fire Dragon - making of - Step 23

next layer... hitting my tablet with pen a lot :-)
 
Fire Dragon - making of - Step 24

setting layer mode to overlay...
 
Fire Dragon - making of - Step 25

next layer...
 
Fire Dragon - making of - Step 26

setting
 
layer mode to overlay...
 
Fire Dragon - making of - Step 27

Next step - volcano. As with previous mountains, set color to black, and use Pen tool to make a shape of a mountain.
 
Fire Dragon - making of - Step 28

In new layer, use large soft brushes (from dark red to gold) to fill mountain with color. Create clipping mask (from layer menu). Apply gaussian blur if needed.
 
Fire Dragon - making of - Step 29

Add lava in the same way as with dragon wings - with small white hard brush.
 
Fire Dragon - making of - Step 30

You guessed it right! set layer mode to overlay :-)
 
Fire Dragon - making of - Step 31