Just a quick graphical illustration.
Green is input-signal. The signal are all with 10nF cap, and the resistors are 4.7K, 10K and 100K. The 100K is just to show the effect.
The higher resistor-value, the more stable output. But too high resistor will give problems with noise and voltage-divider between the resistor and input-impedance.
10K resistor and 10nF should be a fine place to start. If you don't have stable current-readings, you can increase it.