Apart from networking, knowing plenty of other musicians/MD's/fixers and such, good solid playing is the order of the day.
Good ears/busking, good reading chops, and picking up things very quickly along with being musically versatile,
and feel comfortable turning up and playing with complete strangers [they won't be after a while if you are doing your job right]
Fretless and Double Bass help, and Bass Synth won't do you any harm.
All these things help elevate you if you wan't to make a [good] living from it.
Basically these days a good all round freelancer will not just be doing [recording] sessions,
It means playing/depping on shows, functions, cabaret/act backing, pub gigs, or any thing thrown your way.
If none of the above phase you, go for it.
Garry