Improve the render quality of fluids

Here are some suggestions for improving the quality of your fluids renders:

Under Shading Quality, set Render Interpolator to smooth for a better rendered look.
If you see chatter when rendering an animation, increase the Quality attribute until the chatter goes away (expect renders in the order of 40 minutes for NTSC frames).
To eliminate software render artifacts, lower the Density Scale until the artifacts are no longer completely opaque, and the adjust the Opacity curve so that the relative densities of the different parts of the fluid are satisfactory.
To eliminate artifacts when rendering with mental ray for Maya, increase the Quality factor under Shading Quality to 2.5, or switch the Sample Method to Adaptive.