Part of what makes a "good" mixture is the ability to hold some moisture, allow air to the roots and resist compacting. This is the reason that many bonsai mixtures consist of a fair amount of inorganic.
A good source of information is Bonsai4me.com
Lots of good info on specific tree species, watering, soil, repotting, training, etc. It's the first place I refer to in regards to any questions I have.