Proper way to plug in generator cord?
Since you have a proper transfer switch, you can safely connect the cord to both the inlet and the generator. As long as the switches on the transfer switch are in the LINE position, there should be no load on the generator.  

Once you start switching from LINE to GEN, then the generator will start picking up the loads.  



NOTE:

I'm not sure how your transfer switch is wired, but there should be no requirement to turn off the circuit breakers in service panel. The switches on the transfer device should handle that.  They should actually break the circuit when switching between LINE and GEN.  The switches will typically have three positions (LINE, OPEN, GEN), so that the circuit is always open before switching to one of the power sources.



Think of your transfer switch as having six contacts, with a shuttle that moves between two at a time.



When it's in the LINE position, the load is being supplied by the power company.



Since there's no load on the generator, you can plug it in and start it up.



As you switch to generator power, the transfer equipment will open the circuit as you switch.



When it finally reaches the GEN position, the generator will pick  up the loads.



So as long as the transfer switches are in the LINE or OFF position, you should be fine to start the generator with the cord connected.