What exactly are people doing with their fleets? I'd love to join one, but I'm not sure what life in a fleet is like.
If you've played other MMO's, Fleets are essentially the same as Guilds in other games, and like those guilds, tend to have a certain atmosphere based on the people in the Fleet. For instance, the Fleet I'm in, Crimson Phoenix, is basically the STO version of our PA from SWG. While currently, it's more of an avenue to converse among friends, we do get together and group up for missions and such. About the only really hard and fast rule we have is that we get along, no drama and be willing to help out. Other than that, you can basically do your own thing.
That being said, sometimes the most difficult thing to do in an MMO is to find a suitable Fleet to join and stick with. There are so many varieties and each has their own personality, it can be tough to find one that you can mesh well with. Some are very open and casual about who they invite, some are very selective. Some are very strict in what you do, some not so much. Some will take someone on without learning about them, others put you through a selection process. But, no matter what Fleet you find yourself in, you need to make sure that it's going to fit your needs and amount of effort you wish to put into one.