My main switch group contains (left to right) Master, Avionics, Alternator, Autopilot, Pitot Heat, and Fuel Pump. The idea here is that the first 4 will almost always be switched on in normal flight. The next two will be used on occasion. The fuel pump switch is farthest to the right because it's easier to reach while my hand is on the throttle.
I have another group of switches for lights, and yet another group for trim functions (On/Off/Reverse and HighSpeed/LowSpeed).