On some cruises, formal dinners or parties are part of the fun. If you don't woen a tuxedo, many ships offer rental services. But even on the most formal of ships, a dark suit and tie are fine for the dressiest occasions. Cruising is ideal for people travelling alone, because it's so easy to meet other people. Most ships have parties just for singles early on, so you can start to be involved right away.
Most ships also have single cabins as well as single rates for double staterooms.
In many cases, a cruise line will even find you a roommate to share a double. Most ships have 110-volt outlets in the staterooms. And many ships will supply hair-dryers in your cabin. But it would be sensible to take an adaptor. On some ships, especially the new mega-liners being launched, dining rooms can accommodate all passengers in one seating.