Best way to do it is to run the generator through a transfer switch, the switch wires to selected breakers in your main panel and the switch is fed by a large single cord. Individual switches on the transfer switch select between your utility power and the generator power. The transfer switch wires to your ground buss and it's recommended to also ground the generator.

My installation has a 6-circuit transfer switch but you can get them with more circuits. I didn't ground the generator and that doesn't affect its operation.