Missions are the big earners - short range VIP sightseeing especially so, though hauling out of extraction economies are also sometimes very high pay.
For other options:
Mining: lots of pristine metallic or ice mining opportunities.
Trading: there are lots of high-tech systems and lots of service economies. You can make ~4k/tonne taking medical diagnostic equipment from a high-tech to a service economy in Boom. (Catch: the service economies are all outposts, and there's no reasonable good to use on the return route; you may be better looking for 2k/tonne routes that work as a circuit)
Bounty hunting: the usual mix of sites is available. Kojeara has some unauthorised installations which are generally better than a HazRES or CNB for payouts. There are also plenty of warzones.
Exploration: you'll start getting first discoveries only 100 LY out, and there are plenty of high value terraformables, WWs, ELWs and neutron stars about.
However: if your motivation for avoiding missions is the effect on player faction BGS, bear in mind that any activity that makes you money will also affect the BGS - it's not just missions.
If you want to avoid affecting player factions much, there are still five systems which don't have any at the moment, so you could just do all your work there. Colonia, Ratraii and Tir make a decent cluster with a mix of opportunities, with longer trips to Einheriar and Pekoe possible.
(Additionally: Tenjin, Trakath, Saraswati, Coeus, Ra' Takakhan, Macrath and Randgnid have player factions present but those factions have generally been present for a while without making overt attempts to control the system, so you are at least for now probably not going to tread on any toes there either)
