Ficus don't like to dry out completely but also don't like sitting in water either. I use a standard well draining bonsai soil with a bit of additional organics (pine bark). Water just before the soil is dry, give it lots of light (outside during the warm months but not below 50°F).
If you live anywhere near Flemington, NJ stop at Allshapes Bonsai near Ringos (just off Rt202). They grow a good number of tropicals and can help you with soil.
http://www.allshapesbonsai.com/