Hi Marcello,
There is no single configuration that will work for every rendering! You will need to experiment to find the best combination depending on how you want it to look.
Look at the help files that come with ArchiCAD for a basic explanation of the Lightworks rendering controls. It is also worth looking through the 'Presentation' forum for some ideas and recommendations (especially Dwights posts) here -
http://archicad-talk.graphisoft.com/viewforum.php?f=3
You can ask more specific rendering questions there too.
Also be aware that your computer barely meets the recommended specifications to run ArchiCAD and will be very slow to render anything. At minimum, consider adding more memory if you will be doing a lot of rendering.
Good luck!