Auto-Ranging Meter Design

OpenCircuits input protection discussion:

http://www.opencircuits.com/Input_protection

It basically boils down to some resistors to limit current and a zener to limit voltage with a couple of capacitors thrown in.

In this scenario you would usually use a combination of zeners and diodes to protect the ADC input from excessive voltages. You would also avoid letting even the overload voltage approach the maximum input voltage (e.g. have your meter measure 0-2V and set the overload at 3V for a 3.3V supply.)

Here is another solution that may be more expensive and take more space, but it is something to consider.

You could use an opamp and set the rails of the opamp to be the same rails as the microcontroller. This will prevent the opamp from ever outputting more then what the microcontroller can handle. Then you can use the pot to control the gain of the opamp.