I've found it pretty simple to start furballs, but sustaining them is a different matter.
To start one, just take a friend and head to an enemy field nearby where there's already some action (take 100% fuel). Then split up, staying out of icon range of each other (but on vox) and loiter at about 5-7K. Stay close enough to the field to keep it blinking. When a pilot lifts, let him get out of the ack, and climb to your alt, or until he's comfortable enough to come after one of you.
Fight him, and kill him 1v1. You have to kill him once or twice without dying yourself, or he'll just land and go elsewhere. Often, he probably doesn't even have fuel to do much more... You (or your friend) need to stay out of icon range and leave you alone. Let your opponent have a good chance.
When he dies, 9 times outta 10 he'll lift and try again. Repeat the process. Eventually, a 2nd, 3rd, maybe 4th plane will lift. Continue the process, but take it further from the field. Regardless of the temptation, do not chase them to the ack. Let them go if they want it. Let them have it as a safe zone. No vulching!
At this point, dar will be building, and I can't remember the last time this happened and there wasn't a stream of friendlies on the way to allow your egress for fuel.
The key to it is a steady stream of players from both sides. No big missions. A big swarm with a "purpose" will kill the fight. They'll arrive with the enemy too spread out to do much, and will overwhelm the fight. Once the furball has been going on for 10 minutes or so, heavy fighters and bombers are a real plus, as long as they aren't in it to shut the field down.
Leave a few hangers up. Leave the GV hanger up. Leave the radar up...
Two guys can start a furball with little trouble. Eventually, it'll get squashed, but it was fun while it lasted! Go start another... Once a furball dies, it's the easiest time start another. All of the players are still around, they just need to see another fight begin!