To balance the chicken remove the motor from the bracket and place the rotisserie rod with the chicken on the grill so that it moves freely. The heavy side will drop towards the bottom. Pull the counter balance straight up and tighten. It won't balance perfectly, but you will offset the weight enough to allow the motor to handle the load easily.
Now attach the motor and turn it on. Make sure that the chicken doesn't move on the rod and that it turns easily. Once you have determined that it will stay put, you can start the grill.
Rotisserie chicken is grilled indirectly. This means that the burners directly underneath the chicken are off and that all the heat is being provided by the other burners. If the burners under the chicken are on, you will get flare-ups.
Adjust the heat on your grill until the temperature reaches around 350 degrees F. It is not a good idea to wander away too long. It is best to keep an eye on the chicken for the first few minutes to make sure that everything is going right.