Since blowing my overdrive up I've done a fair bit of reading about this style of overdrive and there's a few things you should bear in mind. First of all a 4 speed is going to be a lot harder on the overdrive because there's no torque converter to soften the blow when the cone clutch engages. When driving around town I tend to dip the clutch just after I hit the switch because at low speed/part throttle it bangs in even harder.
With the overdrive switched out, the drive is taken up by a one way roller clutch when accelerating or cruising so it's not going to slip. In reverse or on the overrun, the one way roller clutch does nothing and drive is through the cone clutch which is held against the annulus with low fluid pressure. The cone can slip under heavy acceleration in reverse or on the overrun so engine braking should be avoided if the overdrive is switched out. When the overdrive is engaged, the cone clutch is held against the clutch band using very high fluid pressure (about 700psi) so it's not going to slip on the overrun. With that in mind I always slow the car down with the overdrive engaged and let it drop out automatically at about 15mph.
The other thing I do now is regularly change the fluid. There's a drain plug fitted as standard to my overdrive so I don't even have to drop the pan and it only takes about half an hour.