I don't know of any manual, but I've found the youtube tutorials very helpful.
https://www.youtube.com/playlist?list=PLnXY6vLUwlWVsI6mb8Txb6MYZ4wdGdvaA
Along with the sample projects
http://www.graphisoft.com/archicad/archicad-18/rendering/#sample-project to see a bit more in depth what the settings are.
For surfaces I am generally working with the library of preset surfaces, either using them as they are or doing small adjustments.
It took some time for me to find settings for quick, acceptable renders, as we generally do a lot of renders throughout the design process for quick presentations to clients and for permits etc, but with help of those videos, the sample files and some experimenting I'm getting ok results.
I haven't been doing any superglossy artist impression work yet, though. I'm expecting that to take some learning time too!
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
Windows 10 Pro
Adobe Design Premium CS5