Help on ranking up my backburner

I just ranked up my backburner to server clearing but it took since last December to do so. So how can I double the kills tracked (without strange farms).

Tips like good maps, team comps, secondaries, strategies and counters to the more difficult classes like heavy or soldier.

Before anyone slams me for being a pyro main who wants to farm kills for my strange, please remember I'm using the backburner, and not the Phlog