hi there
generic is a difficult term to use when describing soil,
its kinda like saying "ive got a generic car, how do i improve it?"
you could add leather seats, cd player, light-weight rims, performance exhaust, metallic paint, ecu upgrade, better tyres etc...

from my experience its all about texture, you dont want it too muddy, or to heavy, you want it to drain well, but not dry out too quick, and you want to have good air penetration.

to much vermiculite can be bad( i found this out the hard way), and make a muddy soil even muddier, hence less air-penetration. maybe you need more solid matter with air retaining properties? maybe the addition of a bit of sand and some perlite will help give the soil more structure, its hard to say without knowing whats wrong with the soil that your currently using...

theres lots of people on here with much more knowlege than i, but its hard to fix a problem if you dont know what the problem is....can you explain a bit more?