For my application, the output signal should be extremely smooth. I am using this voltage regulator:
which is a very nice piece of electronics but I’d like to smoothen the output signal. Can you recommend the components for an RC or LC filter?
You need to define “extremely smooth”. What is the expected load current range and allowed output voltage variation (RMS ripple and absolute)?
An RC filter may suffice for your application. A general introduction to power supply filtering can be found at http://www.learnabout-electronics.org/PSU/psu12.php