My mum swears by whisky . . . just soak a cotton wool ball in some and your gold will come up a treat. Best not use the 25-year-old single malt, though.
Gold does not tarnish, and should come clean using a clean, soft dry cloth. Ingrained dirt due to intricate detailing on gold pieces can be cleaned using a toothbrush or similar with a litttle water.
I have an ultrasonic bath which does an excellent job of cleaning such items and can be puchased from the likes of Enerst Jones and other retailer for about �20
My grandfather was a jeweller and he taught me the best way is to use luke warm water with fairy liquid, slowly brushing the gold until it is clean. This also works well on precious stones as well. Cheap but very effective i pormise.