I don't know if this has been shared before, but in cases where max precision is more important than min friction, it may help to route gears double (with equal ratios of course) and have the closed circuit skip one or more teeth somewhere in the circuit. That way you can have the slack in one route compensate for the slack in the other route.
When you route gears double, the gear meshes together make a closed circle. Before installing the last gear in the circle, you can sort of wind up the adjacent gears against each other to eliminate slack in the rest of the circle. Now when you install the last gear while the adjacent gears are wound up, you get a closed circle with only very little slack in it.
With the number of 'skipped' teeth I refer to the number of teeth by which the adjacent gears have been wound up, compared to their positions without wind-up.
In this simple circuit I skipped 1 tooth to obtain a transmission with practically zero slack: