Here's my view of a planes C/G. It may not be right but it has worked for me with every plane I have flown.

I'm looking for a plane that flies the same upright or inverted. Most all the planes in my hanger have airfoiled horizontal stabs, which means they are lifting surfaces. The purpose of a tail mounted lifting surface (stabilizer) is to counter the weight of the nose. I want the tail of my planes to fly with zero trim input because any offset of the elevator incurred from trim translates to drag, wastes power, and any trim one direction will need to be countered in the other direction. The difference between upright and inverted if you will. All this is determined at a "medium" flight speed. The reasoning there is that my planes have plenty of power to maintain level flight at a medium speed and any required increase in power is intended to either climb and/or perform a vertical maneuver, or help counter the effects of gravity in a bank. My planes don't need anywhere close to full power for level flight maneuvering.

The best way I have found to locate and use that zero horizontal stab trim point is by moving the C/G. If the C/G is too far forward the tail will need up trim, too far aft and down trim is needed. Either way if I have a few clicks of trim in one direction I'll need to fight it with stick input when the plane is rolled over. So regardless of where any manufacturer states the C/G should be located I'll alter that location until I have zero elevator trim to fly the plane straight and level. Most manufacturers use what could be called a "safe" C/G location in the area of 25 to 27% of MAC. It's almost impossible to have an unstable plane in that area. Unfortunatey that's usually nose heavy, much too stable, and they require a faster approach speed to prevent what some might call a tip stall, need to fly faster through manuevers to prevent breaking off to one side or the other in a tight maneuver, and "float" down the runway while bleeding off flight speed. It creates much too much work to have fun flying like that.

After all that has been done I'll move on to other types of trim or mixing. Typically after the C/G is established all the rest of the trimming is pretty easy to do. The C/G effects everything the plane does so there's little point in dealing with engine thrust offsets or coupling mixes until the C/G is "happy". Which takes us back to why I prefer a zero/zero initial engine thrust line. I can't know what it needs until the C/G is established. It's easy to trim a plane that starts out "neutral".