Well for normal fire I usually start painting Scab Red, then Red Gore, then 1:1 Red Gore:Blood Red. For each color change I pick out the next highest layer so the outermost is the brightest. Then I Red Ink all of it (I guess Baal Red wash is the new red ink in wash format). Then I pick back up with Red Gore, 1:1 Red Gore:Blood Red, then Blood Red on only the highest points. Then a little Orange scattered about and a little yellow scattered about just to draw attention to different points.
But honestly, I'd go green for something different.
I'd start Orkhide Shade foundation, Knarloc Green, 1:1 Knarloc:Camo Green, Thraka Green Wash, then Knarlock, 1:1 Knarloc:Camo Green, Camo Green, and then highest points in Snot Green.
More layers = better looking fire with any scheme you do.