Take any your scene, enable corona environment add some basic materials, leave render settings at defaults, render and go on from there, explore yourself... IMHO there is not much to explore, corona is very simple to control and defaults are very well set as a universal starting point.
The values that you might be mostly interrested in are:
Path tracing samples: use higher if your scene is to be lit mostly using GI bounces(don't go over 64-my opinion)
Lights samples multiplier: use higher when your scene relies mostly on direct lighting and has many shadows directly from lights (I wouldn't go over 16 but again it's my personal opinion)
Changing these settings won't compromise quality AFAIK, it will only affect how fast your render will be clean(so take a look on how your scene is set-up and how is your lighting set-up)
Any deviation form default settings will be subjective setup for specific demands by specific person using specific HW..
Unlike most renderers, with corona it's really not that time consuming to figure what works in different scenarios by yourself.
Try to avoid tweaking randomly some values in render settings (before you even try defaults) and complain here that it is too slow.
I personally have a feeling that people are used to search for some ultimate setup before trying defaults because vray and mental ray defaults are "not much of use".
Anyways, I'm no corona expert so please take it as just some opinion on the matter :)
