Like JT says there is no one way to do it lighting, but here is my advice:

-light on side of forges: good start here; the reason its not looking great is due to the fact that you have added highlights but no shadows. The northern forge looks good but you should reduce the size of the highlights to 1/3 of the thickness like the southern one. Then add a layer over this, where you draw with a fat fuzzy black paintbrush over the western third of each forge. Then reduce the opacity to c. 30% to create a shadow layer. The reason you would not use as overlay layer to create this shadow layer is because it would intensify the already-saturated colour of the forge edge.

- Like JT says the anvils really do look great. The shadows are unrealistic but that's ok. They are also too fuzzy - they need to be sharpened-up by 50% to look more like anvils from the side, and perhaps you can lighten the shadows very slightly. The lighting effect on the northern anvil is very good (I don't know why you are not happy with it - I love it!) and should be added to the southern one. After this, add a second highlight layer using the colour orange and set on overlay (60% opacity) and with a small fuzzy brush go over the sharp edges of the anvil closest to the flame. Then do it again (but don't duplicate) with a very pale yellow. That should work. Also add these yellow-red highlights to the edge of the forge stonework to a lesser extent.

- Agree with JT on the flames. The colour is very good though ; it just needs a little variety - add several layers of patchy black overlays (maybe using a 'turbulent' plasma-filter layer mask or similar) to deepen and darken the fire colour in places.

-shadows and highlights - just add a LOT of these, doing them all by hand. I'd start off with a lighter floor shade, and add a hint of brown/beige to the floor (tip: increase the brightness and contrast of your floor layer quite a bit, then add a layer of pale browny-beige-orange on top set to burn and 40% opacity, it should work) to fit in with the forge edges. Then layer on your shadows and highlight if you add too much colour to the floor you will need to make your shadow layers normal rather than overlay).

-I made some fiery-shadowy maps a while ago that might give you some ideas - follow the link to my Nightwyrm Fortress maps below and check out maps D1-D5.

-Keep the furniture sparse. Don't go for a cluttered realistic forge with dundjinni furniture - the clash of colours and styles will make the map look crap. If I were you I would add nothing to this map at all.