The University of Calif. and many other organizations have great literature/info regarding this subject of soil mixes. Also, there is info online with the "other" tomato site and the "other" gardening site. Trial-and-error is my best teacher. Cole has some good ideas above....As far as ratios...I think it is really NOT an exact science because of the many variables (ie: crop grown, weather, locale, available sun hours, etc). Many products like perlite and pine bark appear to simply be "aerification type fillers"...their biggest value is really to provide an area that allows the roots to grab water and nutrients within it's structure. This principle is where products like "MiracleGro Moisture Control" goes too far. The polymer ball-like structures retain too much moisture for most container applications, and the plants do not have the water/nutrients available 24/7...if you know what I mean.
PS (added later) We have not scratched the surface as to nutrients for containers. Again, Cole (above) has brought some good ideas to the table. I would recommend learning exactly what a "complete" fertilizer is. Trace elements added are of most importance when container growing.