This site is quite helpful:

http://carnations.org.uk/varieties/varieties-of-perpetually-flowering-carnations

Personally I find a 50/50 mix of vermiculite (I use the cheap stuff sold for loft insulation) and peat-based or peat-free compost a good mixture for all cuttings.
A bit of bottom heat always works wonders if you can get a cheap heated propagator.