Before you Declare War, here are some rules:

Rule #1 No God-Modding
This is by far the most common rule in RPing, so if you're an RPer then you know God-Moding is illegal, even here. that means no controlling someone that doesn't belong to you, or saying what they do for them. That also means you're OCs and Characters cannot be invincible and cannot seem to be so.

Rule #2 If you waste Resources, you will run out
An endless swarm of Ships and fleets is allowed. but just remember: One planet can only supply so many ships, so keep that in mind.

Rule #3 Genesis and Genocide are allowed
If you have the technology, you are allowed to send super-weapons to destroy you enemies. There will be a limit to how many you can send depending on what the super-weapon is. Likewise, you are allowed to blow yourself up and annihilate your own Nation if you feel the need to. ((though, why you would feel the need to is beyond me....))

Rule #4 Take Boundaries, and Territories into Consideration
If you pick a fight with another Civilization, you can't just automatically start a battle right at their homeworld. Unless the Civilization is set up where the their homeworld is right at the border, then you have to break through the defenses to get to their homeworld. Also be aware that Galactic landmarks must also be noted if you attempt to do battle with someone.

Rule #5 There ARE other ways to fight besides Guns
You can raise an Armada, charge into your enemies territory, then smash through every one of his ships and planets till they surrender or you take control of their homeworld.....
OR you can wage war differently.
Espionage, Politically, Galactic Influence, Sabotage. these are all allowed, so long as you can pull them off.

Rule #6 Punishment
Failure to comply with these rules will force the Guildmaster here to inform you that you Homeworld's star went Supernova and obliterated 99% of your Civilization(or your fleet) so don't break the rules.

Knowing all this, good luck waging war.