Below is an example of house rules, from Frans Slothouber's GalaxyNG server.

Galaxy House rules

Rules for Players

Behavior that is not allowed:

[1] Using another player's password to send orders without that player's
[2] Using another player's password to request a copy of that player's 
    turn report without that players consent.
[3] Trying to crash the server.
[4] Gaining access to the server and/or reading the game data files.
[5] Out of character verbal abuse of other players. Remember it is just a game
    and people are just playing a role.
[6] Playing more than one nation in a game. It is allowed to do this
    for a short time to help out an ally that is on vacation. However you
    should notify the GM before you do this.
Sin against any of these rules and you are expelled from the game.

Behavior that is considered bad:

[7]  Joining a game and then dropping out after a few turns.
     Joining a game implies an intention to play the game through to the end. 
     Leaving a game without a good reason is considered very disrespectful. 
     Don't join unless you are willing to commit yourself to an entire game, 
     which may take several months. 
[8]  Giving your planets very offensive names.
[9]  Attempting to influence a player's behavior in one game by offering 
     threats or concessions in another game is called "cross play". 
     This is strongly discouraged. 
[10] Forming alliances before a game starts.  

There is little a GM can do against this but it won't win you any friends.

Behavior that is allowed:

[11] In-game and in-character everything is allowed.  If you can express it 
     as a set of orders it is allowed(1).  Provided you do not sin against 
     [1], [2], or [3].

     In-character, that is in the role of leader of the nation you are
     playing, everything is allowed.  So you can lie and cheat, come back on
     agreements, or send a mass 500 warship while claiming you are only 
     sending a small cargo ship.  

     You are also allowed to do this out-of-character, but you will not make
     many friends that way. If you want to enjoy galaxy for a long time make
     sure that you clearly identify when you are talking in or out of

Exceptions to the rules for Tiger games:

[12] Rule [10] does not apply.
[13] Rule [6] does not apply provided you play a nation in the same team.
[14] The team leader can remove a player from the team and give the nation
     to another player.

Rules for the GM:

[a] GMs are to remain scrupulously impartial in all matters. 
[b] GMs should not change the parameters of the game after players start 
    signing up for the game unless the players unanimously vote to do so. 
[c] It is more important to run a turn correctly than to run a turn on time.
    So in case of any trouble the GM will delay a turn until the problem is
[d] GMs do not play in the games they host.