My next boat will have a jack plate. I have never had a boat with one. Is there a rule of thumb as far as finding the sweet spot or is it just driving the boat and trying different positions?

There's a bit of a science to it.

If you go to setups on the BBC and provide all the pertinent details - hull, motor, prop, set-back, etc someone usually has a good starting point to set your prop-shaft below pad - i.e. they might say start at 3" PTP and adjust up in 1/4" increments until your water pressure drops then drop it an eighth.

of course you also want to pay attention to how it handles, turns, hole-shot, all that. if it cavitates with trim set properly for the operation you may need to drop it.

If it's a manual jp then it's trial and error until you find a sweet spot. If it's a hyd you can adjust on the fly for water or load conditions

There is a lot of science to it. The whole idea behind the setback jackplate is to allow the motor to sit off the transom so the prop bites in "cleaner" less turbulent water. The cleaner the water the prop is turning in, the better bite it has. The better bite it has, the more efficient it is.

Here's the rub. Bass boats are nose heavy as a general rule so you need a prop with lots of bow lift most of the time. The more weight you put in the boat, the deeper in the water you have to run the prop to attain optimum efficiency. The deeper you stick the lower unit in the water the more drag you have to overcome.

Some hulls like Bullets, Allisons, and Strokers have more aerodynamic lift built into them than others but they tradeoff stability at rest or "fishability" The best thing is to buy a hydraulic plate so you can adjust the motor height to the load.

Ted gave you some good advice above to look at BBC to see what a good starting point would be for your hull/motor combo.

But be forewarned, you can spend a small fortune (experience talking here) on trying to obtain the last 0.007 mph from your rig. In the end you have to ask yourself, is it worth it??