How to make LM39302R (voltage regulator) work?
I don't know this part specifically, but regulators usually require decoupling (bypass) capacitors on their inputs and outputs. Check the data sheet and, if available, an application note for details of what is required. A quick look at the data sheet shows that these are required.
On your last part about the absolute value of the resistors, yes there are some very practical points that the simple equation hides. The device itself will place a small load on the circuit, so check for any specification of leakage current, or internal resistance. If your resistor values are too high then the leakage will become significant an cause errors in the voltage divider. Too low and you will at a minimum be wasting power.