Star Kingdoms has a built in message system, where you can send a private message to a person by going to his or her sector and clicking on the small icon looking like a tiny envelope, to the right of his name. You can also use the game's built in alliance- and sector forums, and the public forums to talk to other players.
Most big and organized alliances also have external alliance forums, and a lot of persons use different chat services (ICQ/AIM/MSN) to communicate with their friends and sectormates. The most commonly used in SK is AOL Instant messenger, so if you are new to SK, try downloading that one (from www.aim.com), if you want to make friends and get to know other players fast.

Sector Leader or Alliance Leader
If you want to be sector leader or alliance leader, you should be prepared that you will have to spend a lot of time messaging people, replying to incoming messages, sorting out diplomatic problems in chats, and making decision. it is not just to create an alliance and hope that someone will join, or ask people to put their SL votes on you, so therefore, it is usually better if you aren't any of those two things in your first games, but wait until you first know the game and have some contacts, before you try it.
Being the first person in the sector and the one taking care of everything, at the beginning of a game might help a lot if you're aiming at becoming SL. A few of the threads which are usually good to create at the beginning when the forum is empty are:
•Welcome - a thread where you just welcome everyone and where people can sign in even if they don't have anything they want to say.
•Sector Leader - a thread where people running for SL will explain why they should be voted for. If you want to be SL, see SL message below.
•Alliance - a thread where to discuss what alliance the sector should join. Even if you become SL, you shouldn't be a dictator.
•Contacts - a thread where people can post their contacts.
•Sectorname and sector picture - a thread in which to discuss sectorname, and sector picture (a remote hosted picture which is shown above the sectorname). If you need anywhere to host it, www.angelfire.com is a service where you can get a free account to do that with, for example.
•Bar - a thread where people can just post for fun and get to know each others.

SL message
If you want to become SL at the beginning of a game, some useful things to write in the thread where sector leadership is discussed are:
•A little bit about yourself in real life.
•When you started playing, previous kingdoms and sectors, if you still remember that.
•How much time you usually spend online, and where (in what time zone) you live.
•Achievements in previous games. Have you been ranked in top 100 before?
•If you have been SL, VSL, alliance leader, or had some other important responsibility in a previous games.
•Other reasons why people should vote for you.

About talking to people in SK, it is your own choice how you want to act or how social you want to be. However, it is never a good idea to insult other players or make enemies, since offensive messages can be reported to the admins, which might disable your kingdom because of that.