Some tips for the gold:
Gold is actually not yellow in colour. Gold nearly exclusively relies on reflections to give it its look. Therefore you need a good environment that can be reflected. The trick is to tint the reflections depending on the viewing angle (using a Fresnel-Effect shader in the reflection channel). Tint it with a Fresnel gradient that goes from a dark orange to a light yellow. Another thing that good gold has is a reflected environment that has both very bright and very dark areas. Gold lives from a bold contrast. Highlight is metallic, very shapr and bright maybe with a hint of anisotropy.
Good reference image for gold would be
this one here. Notice that there are areas on the gold that are completely black and others that are nearly white. Inbetween is everything from dark orange to bright yellow.
Another tip for your render - try to put some ambient occlusion on your image. That's basically for all renderings. If there ever was a "Make Cool"-Button in a 3d programm it would definatively lead to Ambient Occlusion. It just makes your image better in (nearly) all situations.