Ok. so this isn't so hard.  Make an image, doesn't matter what size, doesn't matter.  Give it a black background, that should be cool.  I used 139X131.  After all that, create a new layer.

  Alright, simple enough.   Pick a color, red, blue, yellow, green, whatever the hell ya want, it's your image.   But please, make a note!  Don't use a pure hue (color).  You have to use a color tint, tone, or shade for this to work...the dodge and burn tools don't work with pure hues.  For this image, I chose green.

  NOW, using that color, make a circle, make it so it almost touches the end of the image (this is so the flames go far).  Put that sucker smack damn in the middle.

  Ok, make a new layer.  Add a black circle smaller than the first circle, and put it in the middle.  Make it so there is enough space that you can see a significant amount of color (enough to add some flames)  Look at the example to get an idea. 

  This is where the artistic talent comes in :) 

  Grab up the dodge tool, set exposure to 80-90%.  Select the big circle layer, and slowly and carefully brighten around the edges of the black circle.  Brighten untill it is a crisp white.  Then select a larger brush and set the exposure to 10-15% and brighten the rest of it...not too much now. 

  Try and make the brightness blend in, like a gradation.   Eventually, you should come up with something like the example.

  Now it gets alittle complicated.  This is where your creativity comes in.   Use the eraser, select a small blurred brush.  Set the opactiy to about 70-80%, and delete some of the color around the edges in a jagged kinda way...as demonstrated.  But, hey, play around with it.  Who's stopping you?

  Alright, cool.  Whip out the burn tool.  Set it too a small brush (this depends on the image size, and how big of flames you want.), and set the exposure to 60-70%....

  Now, when you use the burn tool, make sure that when you begin to make your way inward, set the exposure down more and more...you don't want to erase the image!  Try to make it dramatic...make the flames flow...sortof :)

  Don't forget about your dodge tool!  If you darken an area too much you can revive it by using that damn thing. 

  And one more thing, BE CREATIVE.  Mess around with it!   Play around for a while, see what you can get. 

  One more step (I think).  Switch over to the black circle.  Use the eraser, put it to a very low opacity, 10% or less, and carefully screw up the circle so it is not a perfect circle.  This step is optional, but I like to do it just for some added realism.

  Now I made a mistake when I did the example...I had already flattened the image so I had to airbrush in the white stuff "inside" the black circle.  Anyway, it gives a pretty good idea of what you should be doing...but for a really good example look at my gensun image above...that blue thing...yeah, that blue thing.

  The very last thing you should do is get a small ass brush, and zoom in.  Then you can add all the other details in the flames to make them look more layered and what not.  It's up to you though!

  Remember, BE CREATIVE GOD DAMNIT!