I have been having the hardest time making a decent fire material. I’m using the standard two texture system: one for density, one for color and emission. My rendered doesn’t even look as good as the viewport display!
From a similar post a few days ago. I include the pixelation paragraph in case you run into that problem as well.
The pixelation will probably be fixed by decreasing the Step Size under Step Calcuation under the Integration section that appears under the Material panel for the domain object. I think it defaults to 0.2. I use values around 0.005. It made a world of difference. Might depend on domain size etc, so experiment a bit.
As for the fire material, study the materials in the blend files posted here: