Owing to the current geo-political situation, the idea to organise your next trip to Oman doesn't always spring naturally into your head. It's really a shame because apart from the border zone with Yemen, it's a completely accessible destination.
So as to be on the right side of the law, before going on a trip to Oman you must have a passport which is valid for 6 months after the date of your trip and after the day you leave the country. Canadians and Americans require a visa before departure, but citizens of the UK do not. If you want to apply for a visa you should go on the Royal Oman Police website and plan for a delay of several days to obtain it. Even if it says that a visa can be obtained in 24 hours it's best to apply further in advance. There are two types of visa for you. A single entry visa is valid for 6 months after the date it was obtained and allows you to stay for 1 month in Oman. It costs £35. A multiple entry visa is valid for one year after the date it was obtained and thanks to it you can do several trips for 3 weeks at a time. It costs £85.
As for vaccinations, the yellow fever vaccine is obligatory if you have previously stayed in a country included in the area at risk. Otherwise, this vaccine is simply advised.
If you haven't applied for a visa before arriving, don't panic, you can always get one once there. In the country's post offices or in Muscat Airport you can get one easily and will also make some savings. By buying it here the visa only costs £6.50 but you can't stay for more than 10 days in the land. The one which allows you to stay up to a month only costs £28. Each one can be extended by as much and for the same prices. However you can't extend a 10 day visa up to 1 month.
As is the case in many countries, if you want to hire a car there you'll have to show your International Driving Permit which can be obtained from the Post Office for a fee of £5.50.