I can see splotches in my image! [pre-1.0 HD cache]
This guide refers to HD cache that was used in pre-1.0 versions. Newer versions use UHD Cache that shouldn't need additional tweaking.
To get rid of "spots" or "splotches" in your static rendered image:
If you are using HD cache as secondary GI solver, go to Render Setup > Corona Settings > Secondary GI: HD cache and make sure you are using default settings or higher.
If you still see splotches at default settings, in Secondary GI: HD cache > Interpolation accuracy, change Direction and Position accuracy to a higher value (for example 80). Also change Record quality to a higher value (512 or higher).
If the problem persists after tweaking HD cache settings, you can set both primary and secondary solvers to Path Tracing.
Note: this will probably increase render time or introduce noise.
Another possible solution, especially when both solvers are set to Path Tracing is to lower the Max sample intensity value in Render Setup > Corona Settings > Main settings > Speed/Accuracy balance to 10 or less. This will introduce some bias but might lower noise level.
See: Max sample intensity
If you can see flickering or splotches in animation, see: How to setup animation flicker-free?