It has been 50 years since I have ridden 2 up and normally I defer to Black9 on all things motorcycle related however;
Don’t “help” the person on the throttle, just be predictable.
This is no problem if the passenger & the person on the throttle are or opposite genders, the passenger wraps their arms around the waist of the person on the throttle at all times save straight sections of slab.
MSF SAYS AS FOLLOWS.
Instruct passengers to hold onto you at your waist or hips, or the bike's hand-holds. Ask them to lean forward slightly when you leave from a stop or accelerate along the highway.
Also, when you brake, passengers should be firmly braced against your waist and should lean back slightly. You don’t want their weight to shift forward.
Advise passengers not to lean unless you do. You do not want the person behind hanging off the bike at 30 degrees; that will do funny things to the steering. However, when you lean going around a corner, passengers should definitely lean as well. So have them look over your shoulder in the direction of the turn when you go through a corner; that will put the weight where you want it.
When riding 2 up with another guy about the most contact I want or are willing to give is to pinch the jacket of the guy on the throttle with a couple of fingers. – Fortunately when guys ride two up either there is a desperate situation or both are drunk.
Never seen women ride 2 up but would like to.