We researched cruises on the internet and talked to other dancers. There are numerous cruise forums and some of the cruise agencies on the internet have independent reviews. Reading through the reviews you can piece together information about what is important to you. They also have deck plans, but those don't always show the dance floors.
Most cruiselines have lounges were you can dance. But the size of the dance floors varies quite a bit. Also the amount of dance music varies. We have had fun dancing on Celebrity Century and Norwegian Sea, both have decent sized dance floors, for a cruise ships. A lot of the people in the dance club we belong to go on cruises and do a good amount of dancing on their cruises. Many of the others are okay, it's just that Costa is exceptional for dancing. Lot's a great music, lot of real dancers and people who like music.
On other ships, we normally were the only ones dancing most of the time and you have to really understand dance beats, to determine what dances to do, since many do not play standard ballroom music and there normally is nobody else to see what dance they do.
We live in southeast Wisconsin and found the following good dance options.
1. Teachers and studios that have dances open to the people, either at the studio or a public location.
2. Dance Club dances.
3. There are a 3 real ballrooms in the area that have ballroom dances.
4. Special dance weekends held by upscale Hotels.
5. Public dances sponsored by various swings clubs. Swing clubs here tend to by predomontly young people, but there is always a good share of us older people. They frequently include a few rumbas, foxtrots and chachas.
6. A small newspaper in our area publishes a monthly schedule of all ballroom and swing dances in Wsisconsin and Northern Illinois. They also have some of the big band and social dances listed.
7. Other dancers at your dance club also are a good source for finding places to dance.
8. Some colleges like Wisconsin and UW Milwaukee sponsor ballroom dances open to the public.
I am sure there also are people on the forum that may know of options in your area and can help you out.
Good thing is the options are increasing. Dancers dateline now has about double the dances listed, as when we first started getting it 4 years ago.