Many people say that standard Dutch is spoken in Haarlem, about 10 km west of Amsterdam. The original Amsterdam accent has some very specific peculiarities like a very strong S. Not really standard Dutch. Just like Agnes says the G in the Netherlands is strong and guttural. In Flanders though it is produced in a softer way with the tongue lifting in the middle and touching your palate. The R is usually a rolling R or Rhotic R and has no "curly tongue" like in English! The R can also be pronounced as a guttural R, more the case in Flanders because of the closer contact with French.

About G, it sound like "kh" (use your throat also, like you do when you want to spit sputum)