Taboos
Your nation, age, marital status, number of children (if any), religion, occupation, reasons for visiting Oman, and impressions of the country are the typical subjects of conversation in Oman. Omanis take great pride in their country, thus any criticism of it will not be warmly accepted (unless, perhaps, you are simply agreeing with an opinion expressed by your host).
Even more vehemently avoided should be comments that are critical of Islam. Given that concepts like atheism, agnosticism, and alternative religions are not often understood, it is also easy to claim your religion is Christianity when asked, even if you have no such beliefs.
Politics, unless it is of the most broad and harmless variety, continues to be a delicate topic that should only be broached with great caution. Additionally, it is strictly forbidden to criticize Sultan Qaboos.