I'll give you some passenger suggestions, based on having my wife out back for almost two decades now, and having occasional guests on board:
- Have them mount holding your shoulders firmly. (I get on first, get off last.) It's pretty high getting on, and the whole thing may get awkward, and they may not be used to it. You give the OK nod for them to get on and off, i.e., you're ready, your feet are down, your hands on the bars, the front brake grasped.
- Have them mount by putting that first foot DOWNWARD. That is, new passengers often tend to want to pull the bike toward them, which is hard on your legs. Instead, instruct them to be putting their weight, using that first foot, in a downward direction, NOT trying to pull the bike toward them.
- After that mount or dismount, remind them that your shoulders are a no-no, i.e., off-limits. Grasp your waist, or passenger grab rails, or their hands in their laps (if you have a trunk or backrest).
- They should, in, um, Zen terms, "be the bike." That is, they should lean with or merely along the bike, or even lean inside (as they get more proficient), and the head/shoulders goes/looks on the INSIDE of turns. The worst thing they can do is try to sit upright when you're leaned over; this will cause the bike to lean more, running out of ground clearance earlier.
- They should relax.
- They should wave to other bikers, kids, etc.
- You have to be smooth in shifting and braking, to minimize passenger anxiety and helmet clunking. So, you want to plan ahead more than usual.
- Save the demonstrations of your maximum cornering skills, stop-light drag skills, etc., for solo riding.
- Immediately before or after parking, or possibly before U-turns, you may want to have the passenger dismount, especially if your slow-speed capabilities aren't top notch on a big bike.
- No passenger squirming or otherwise repositioning allowed during cornering or slow speeds, or possibly even when stopped at a light. Repositioning should be saved for straight-line riding at speed. By now my wife is well aware that I like to "ride ahead," i.e., slowing for lights well in advance, such that I may not have to actually stop and put my feet down. At slow speeds, you don't need any challenges to your balancing the bike, such as passenger squirming.
- Speaking of that sort of thing, when coming to a stop, it's extremely difficult -- harder than usual -- to go from 4 mph to 3, to 2, to 1, to 0. Those really, almost negligible, slow speeds are a challenge to keep the bike from wobbling. At some slow-speed point -- perhaps 2 or 3 mph -- you have to bite the bullet and just stop (i.e., skipping that last bit of really slow speed).
- If you stop on a hill, you'll probably want to do it with both feet. If you're used to getting going by "riding through" the rear brake, you might want to practice hill-starting by using the front-brake and throttle, simultaneously, in combination with clutch-feathering instead.
- Watch out for off-camber, dropping-away, pavement (or gravel, etc.) at any stops. You'll be supporting a lot more weight, and so you'll want to keep the bike straight up.
- Pump up the rear shock, but don't go overboard. Get attuned to frequent shock-bottoming (not enough air) or too harsh a ride (too much air).
- If you don't do an intercom just yet, develop some signals for potty stops, rest breaks, look at that, etc.
[Edit: forgot this one (and I really do try to tell all of these to new passengers... if I remember everything) : ]
- In the event of a tip-over or crash, try to stay on the bike, hands and feet in. That is, try to let the engine- and saddlebag-guards do their thing, absorbing the brunt of the fall.
Those are my thoughts. Here's a page with four articles of passenger-hauling tips from a professional: