I usually do what Sephiroth does too. Hold the hot glue glob upside down (so gravity is working with you, not against you) and comb it out into flames with some kind of tool till it cools.
I used it for my ghost rider 2099 custom on here. It takes practice but if you start wtih a glob and move the layers and tendrils of glue upward like flames you can get good results and you can use teh tip of the glue gun to help sculpt the shape. It does take practice but the glue is cheap and peels off easily once cool. Then you give it a few layers of clear yellow and red paints and you're set. I also used clear orange paints too.