Most ships have four main cabin categories; Inside, Outside, Balcony and Suite. Within each of these categories you'll find different grades, which basically just relate to where the cabin is positioned on the ship. Many ships offer family cabins that can sleep several adults and children together, but do make sure you check how the bedding will be configured as some cabins will have fixed twin beds or will require you to use upper berths, which are like bunk beds.
An Inside cabin will usually be the cheapest option and is a good choice if you have a strict budget or would rather spend more money on excursions and tours. They can be quite compact but they will have everything you need for a comfortable stay.
Outside cabins will usually be a similar size to an Inside but will have a picture window or porthole. Look at Obstructed or Partially Obstructed views if you have a set budget but don't fancy an Inside; in many cases they still allow a lot of light in and are often a similar price to an Inside cabin.
A Balcony cabin will give you a much larger cabin, often with a separate sitting area, plus the outside space on the balcony itself. They are more expensive but they can be invaluable if you like to have a little bit of space to yourself every now and then.
Suites come in various forms, ranging from fairly standard ones to those with butler service and several bedrooms. They are great if you are travelling as a family or large group as they have extra living and sleeping space, or if you simply fancy splashing out on the most luxurious accommodation available!
Top TipsIf you're prone to getting seasick, try to book a cabin towards the middle of the deck and not too high up as this will be more stable than being towards the front (forward) or back (aft).